Helpviewer/HelpBrowserWV.py

# -*- coding: utf-8 -*-

# Copyright (c) 2008 - 2018 Detlev Offenbach <detlev@die-offenbachs.de>
#


"""
Module implementing the helpbrowser using QWebView.
"""

from __future__ import unicode_literals
try:
    str = unicode       # __IGNORE_EXCEPTION__
except NameError:
    pass

import os

from PyQt5.QtCore import pyqtSlot, pyqtSignal, QObject, QT_TRANSLATE_NOOP, \
    QUrl, QBuffer, QIODevice, QFileInfo, Qt, QTimer, QEvent, \
    QRect, QFile, QPoint, QByteArray
from PyQt5.QtGui import QDesktopServices, QClipboard, QMouseEvent, QColor, \
    QPalette
from PyQt5.QtWidgets import qApp, QStyle, QMenu, QApplication, QInputDialog, \
    QLineEdit, QLabel, QToolTip, QFrame, QDialog
from PyQt5.QtPrintSupport import QPrinter, QPrintDialog
from PyQt5.QtWebKit import QWebSettings
from PyQt5.QtWebKitWidgets import QWebView, QWebPage
try:
    from PyQt5.QtWebKit import QWebElement
except ImportError:
    pass
from PyQt5.QtNetwork import QNetworkReply, QNetworkRequest
import sip

from E5Gui import E5MessageBox, E5FileDialog

import Helpviewer

import Preferences
import UI.PixmapCache
import Globals
from Globals import qVersionTuple
import Utilities

try:
    from PyQt5.QtNetwork import QSslCertificate
    SSL_AVAILABLE = True
except ImportError:
    SSL_AVAILABLE = False

###############################################################################


class JavaScriptExternalObject(QObject):
    """
    Class implementing an external javascript object to add search providers.
    """
    def __init__(self, mw, parent=None):
        """
        Constructor
        
        @param mw reference to the main window 8HelpWindow)
        @param parent reference to the parent object (QObject)
        """
        super(JavaScriptExternalObject, self).__init__(parent)
        
        self.__mw = mw
    
    @pyqtSlot(str)
    def AddSearchProvider(self, url):
        """
        Public slot to add a search provider.
        
        @param url url of the XML file defining the search provider (string)
        """
        self.__mw.openSearchManager().addEngine(QUrl(url))


class LinkedResource(object):
    """
    Class defining a data structure for linked resources.
    """
    def __init__(self):
        """
        Constructor
        """
        self.rel = ""
        self.type_ = ""
        self.href = ""
        self.title = ""

###############################################################################


class JavaScriptEricObject(QObject):
    """
    Class implementing an external javascript object to search via the
    startpage.
    """
    # these must be in line with the strings used by the javascript part of
    # the start page
    translations = [
        QT_TRANSLATE_NOOP("JavaScriptEricObject",
                          "Welcome to eric6 Web Browser!"),
        QT_TRANSLATE_NOOP("JavaScriptEricObject", "eric6 Web Browser"),
        QT_TRANSLATE_NOOP("JavaScriptEricObject", "Search!"),
        QT_TRANSLATE_NOOP("JavaScriptEricObject", "About eric6"),
    ]
    
    def __init__(self, mw, parent=None):
        """
        Constructor
        
        @param mw reference to the main window 8HelpWindow)
        @param parent reference to the parent object (QObject)
        """
        super(JavaScriptEricObject, self).__init__(parent)
        
        self.__mw = mw
    
    @pyqtSlot(str, result=str)
    def translate(self, trans):
        """
        Public method to translate the given string.
        
        @param trans string to be translated (string)
        @return translation (string)
        """
        if trans == "QT_LAYOUT_DIRECTION":
            # special handling to detect layout direction
            if qApp.isLeftToRight():
                return "LTR"
            else:
                return "RTL"
        
        return self.tr(trans)
    
    @pyqtSlot(result=str)
    def providerString(self):
        """
        Public method to get a string for the search provider.
        
        @return string for the search provider (string)
        """
        return self.tr("Search results provided by {0}")\
            .format(self.__mw.openSearchManager().currentEngineName())
    
    @pyqtSlot(str, result=str)
    def searchUrl(self, searchStr):
        """
        Public method to get the search URL for the given search term.
        
        @param searchStr search term (string)
        @return search URL (string)
        """
        return bytes(
            self.__mw.openSearchManager().currentEngine()
            .searchUrl(searchStr).toEncoded()).decode()

###############################################################################


class HelpWebPage(QWebPage):
    """
    Class implementing an enhanced web page.
    """
    _webPluginFactory = None
    
    def __init__(self, parent=None):
        """
        Constructor
        
        @param parent parent widget of this window (QWidget)
        """
        super(HelpWebPage, self).__init__(parent)
        
        self.setPluginFactory(self.webPluginFactory())
        
        self.__lastRequest = None
        self.__lastRequestType = QWebPage.NavigationTypeOther
        
        import Helpviewer.HelpWindow
        from .Network.NetworkAccessManagerProxy import \
            NetworkAccessManagerProxy
        self.__proxy = NetworkAccessManagerProxy(self)
        self.__proxy.setWebPage(self)
        self.__proxy.setPrimaryNetworkAccessManager(
            Helpviewer.HelpWindow.HelpWindow.networkAccessManager())
        self.setNetworkAccessManager(self.__proxy)
        
        self.__sslConfiguration = None
        self.__proxy.finished.connect(self.__managerFinished)
        
        self.__adBlockedEntries = []
        self.loadStarted.connect(self.__loadStarted)
        
        self.saveFrameStateRequested.connect(
            self.__saveFrameStateRequested)
        self.restoreFrameStateRequested.connect(
            self.__restoreFrameStateRequested)
    
    def acceptNavigationRequest(self, frame, request, type_):
        """
        Public method to determine, if a request may be accepted.
        
        @param frame reference to the frame sending the request (QWebFrame)
        @param request reference to the request object (QNetworkRequest)
        @param type_ type of the navigation request (QWebPage.NavigationType)
        @return flag indicating acceptance (boolean)
        """
        self.__lastRequest = request
        if self.__lastRequest.url() != request.url() or \
           type_ != QWebPage.NavigationTypeOther:
            self.__lastRequestType = type_
        
        scheme = request.url().scheme()
        if scheme == "mailto":
            QDesktopServices.openUrl(request.url())
            return False
        
        if type_ == QWebPage.NavigationTypeFormResubmitted:
            res = E5MessageBox.yesNo(
                self.view(),
                self.tr("Resending POST request"),
                self.tr(
                    """In order to display the site, the request along with"""
                    """ all the data must be sent once again, which may lead"""
                    """ to some unexpected behaviour of the site e.g. the"""
                    """ same action might be performed once again. Do you"""
                    """ want to continue anyway?"""),
                icon=E5MessageBox.Warning)
            if not res:
                return False
        
        return QWebPage.acceptNavigationRequest(self, frame, request, type_)
    
    def populateNetworkRequest(self, request):
        """
        Public method to add data to a network request.
        
        @param request reference to the network request object
            (QNetworkRequest)
        """
        try:
            request.setAttribute(QNetworkRequest.User + 100, self)
            if self.__lastRequest.url() == request.url():
                request.setAttribute(QNetworkRequest.User + 101,
                                     self.__lastRequestType)
                if self.__lastRequestType == \
                        QWebPage.NavigationTypeLinkClicked:
                    request.setRawHeader(b"X-Eric6-UserLoadAction",
                                         QByteArray(b"1"))
        except TypeError:
            pass
    
    def pageAttributeId(self):
        """
        Public method to get the attribute id of the page attribute.
        
        @return attribute id of the page attribute (integer)
        """
        return QNetworkRequest.User + 100
    
    def supportsExtension(self, extension):
        """
        Public method to check the support for an extension.
        
        @param extension extension to test for (QWebPage.Extension)
        @return flag indicating the support of extension (boolean)
        """
        try:
            if extension in [QWebPage.ErrorPageExtension,
                             QWebPage.ChooseMultipleFilesExtension]:
                return True
        except AttributeError:
            pass
        
        return QWebPage.supportsExtension(self, extension)
    
    def extension(self, extension, option, output):
        """
        Public method to implement a specific extension.
        
        @param extension extension to be executed (QWebPage.Extension)
        @param option provides input to the extension
            (QWebPage.ExtensionOption)
        @param output stores the output results (QWebPage.ExtensionReturn)
        @return flag indicating a successful call of the extension (boolean)
        """
        if extension == QWebPage.ChooseMultipleFilesExtension:
            info = sip.cast(option,
                            QWebPage.ChooseMultipleFilesExtensionOption)
            files = sip.cast(output,
                             QWebPage.ChooseMultipleFilesExtensionReturn)
            if info is None or files is None:
                return super(HelpWebPage, self).extension(
                    extension, option, output)
            
            suggestedFileName = ""
            if info.suggestedFileNames:
                suggestedFileName = info.suggestedFileNames[0]
            
            files.fileNames = E5FileDialog.getOpenFileNames(
                None,
                self.tr("Select files to upload..."),
                suggestedFileName)
            return True
        
        if extension == QWebPage.ErrorPageExtension:
            info = sip.cast(option, QWebPage.ErrorPageExtensionOption)
            
            errorPage = sip.cast(output, QWebPage.ErrorPageExtensionReturn)
            urlString = bytes(info.url.toEncoded()).decode()
            errorPage.baseUrl = info.url
            if info.domain == QWebPage.QtNetwork and \
               info.error == QNetworkReply.ProtocolUnknownError:
                url = QUrl(info.url)
                res = E5MessageBox.yesNo(
                    None,
                    self.tr("Protocol Error"),
                    self.tr("""Open external application for {0}-link?\n"""
                            """URL: {1}""").format(
                        url.scheme(), url.toString(
                            QUrl.PrettyDecoded | QUrl.RemovePassword)),
                    yesDefault=True)
                
                if res:
                    QDesktopServices.openUrl(url)
                return True
            elif info.domain == QWebPage.QtNetwork and \
                info.error == QNetworkReply.ContentAccessDenied and \
                    info.errorString.startswith("AdBlockRule:"):
                if info.frame != info.frame.page().mainFrame():
                    # content in <iframe>
                    docElement = info.frame.page().mainFrame()\
                        .documentElement()
                    for element in docElement.findAll("iframe"):
                        src = element.attribute("src")
                        if src in info.url.toString():
                            element.setAttribute("style", "display:none;")
                    return False
                else:
                    # the whole page is blocked
                    rule = info.errorString.replace("AdBlockRule:", "")
                    title = self.tr("Content blocked by AdBlock Plus")
                    message = self.tr(
                        "Blocked by rule: <i>{0}</i>").format(rule)
                    
                    htmlFile = QFile(":/html/adblockPage.html")
                    htmlFile.open(QFile.ReadOnly)
                    html = htmlFile.readAll()
                    html = html.replace(
                        "@FAVICON@", "qrc:icons/adBlockPlus16.png")
                    html = html.replace(
                        "@IMAGE@", "qrc:icons/adBlockPlus64.png")
                    html = html.replace("@TITLE@", title.encode("utf8"))
                    html = html.replace("@MESSAGE@", message.encode("utf8"))
                    errorPage.content = html
                    return True
            
            if info.domain == QWebPage.QtNetwork and \
               info.error == QNetworkReply.OperationCanceledError and \
               info.errorString == "eric6:No Error":
                return False
            
            if info.domain == QWebPage.WebKit and info.error == 203:
                # "Loading is handled by the media engine"
                return False
            
            title = self.tr("Error loading page: {0}").format(urlString)
            htmlFile = QFile(":/html/notFoundPage.html")
            htmlFile.open(QFile.ReadOnly)
            html = htmlFile.readAll()
            pixmap = qApp.style()\
                .standardIcon(QStyle.SP_MessageBoxWarning).pixmap(48, 48)
            imageBuffer = QBuffer()
            imageBuffer.open(QIODevice.ReadWrite)
            if pixmap.save(imageBuffer, "PNG"):
                html = html.replace("@IMAGE@", imageBuffer.buffer().toBase64())
            pixmap = qApp.style()\
                .standardIcon(QStyle.SP_MessageBoxWarning).pixmap(16, 16)
            imageBuffer = QBuffer()
            imageBuffer.open(QIODevice.ReadWrite)
            if pixmap.save(imageBuffer, "PNG"):
                html = html.replace(
                    "@FAVICON@", imageBuffer.buffer().toBase64())
            html = html.replace("@TITLE@", title.encode("utf8"))
            html = html.replace("@H1@", info.errorString.encode("utf8"))
            html = html.replace(
                "@H2@", self.tr("When connecting to: {0}.")
                .format(urlString).encode("utf8"))
            html = html.replace(
                "@LI-1@",
                self.tr("Check the address for errors such as "
                        "<b>ww</b>.example.org instead of "
                        "<b>www</b>.example.org").encode("utf8"))
            html = html.replace(
                "@LI-2@",
                self.tr(
                    "If the address is correct, try checking the network "
                    "connection.").encode("utf8"))
            html = html.replace(
                "@LI-3@",
                self.tr(
                    "If your computer or network is protected by a firewall "
                    "or proxy, make sure that the browser is permitted to "
                    "access the network.").encode("utf8"))
            html = html.replace(
                "@LI-4@",
                self.tr("If your cache policy is set to offline browsing,"
                        "only pages in the local cache are available.")
                .encode("utf8"))
            html = html.replace(
                "@BUTTON@", self.tr("Try Again").encode("utf8"))
            errorPage.content = html
            return True
        
        return QWebPage.extension(self, extension, option, output)
    
    def __loadStarted(self):
        """
        Private method to handle the loadStarted signal.
        """
        self.__adBlockedEntries = []
    
    def addAdBlockRule(self, rule, url):
        """
        Public slot to add an AdBlock rule to the page.
        
        @param rule AdBlock rule to add (AdBlockRule)
        @param url URL that matched the rule (QUrl)
        """
        from .AdBlock.AdBlockPage import AdBlockedPageEntry
        entry = AdBlockedPageEntry(rule, url)
        if entry not in self.__adBlockedEntries:
            self.__adBlockedEntries.append(entry)
    
    def getAdBlockedPageEntries(self):
        """
        Public method to get the list of AdBlock page entries.
        
        @return list of AdBlock page entries (list of AdBlockedPageEntry)
        """
        return self.__adBlockedEntries
    
    def url(self):
        """
        Public method to get the URL of the page.
        
        @return URL of the page (QUrl)
        """
        return self.mainFrame().url()
    
    def userAgent(self, resolveEmpty=False):
        """
        Public method to get the global user agent setting.
        
        @param resolveEmpty flag indicating to resolve an empty
            user agent (boolean)
        @return user agent string (string)
        """
        agent = Preferences.getHelp("UserAgent")
        if agent == "" and resolveEmpty:
            agent = self.userAgentForUrl(QUrl())
        return agent
    
    def setUserAgent(self, agent):
        """
        Public method to set the global user agent string.
        
        @param agent new current user agent string (string)
        """
        Preferences.setHelp("UserAgent", agent)
    
    def userAgentForUrl(self, url):
        """
        Public method to determine the user agent for the given URL.
        
        @param url URL to determine user agent for (QUrl)
        @return user agent string (string)
        """
        import Helpviewer.HelpWindow
        agent = Helpviewer.HelpWindow.HelpWindow.userAgentsManager()\
            .userAgentForUrl(url)
        if agent == "":
            # no agent string specified for the given host -> use global one
            agent = Preferences.getHelp("UserAgent")
            if agent == "":
                # no global agent string specified -> use default one
                agent = QWebPage.userAgentForUrl(self, url)
        return agent
    
    def __managerFinished(self, reply):
        """
        Private slot to handle a finished reply.
        
        This slot is used to get SSL related information for a reply.
        
        @param reply reference to the finished reply (QNetworkReply)
        """
        try:
            frame = reply.request().originatingObject()
        except AttributeError:
            frame = None
        
        mainFrameRequest = frame == self.mainFrame()
        
        if mainFrameRequest and \
           self.__sslConfiguration is not None and \
           reply.url() == self.mainFrame().url():
            self.__sslConfiguration = None
        
        if reply.error() == QNetworkReply.NoError and \
           mainFrameRequest and \
           self.__sslConfiguration is None and \
           reply.url().scheme().lower() == "https" and \
           reply.url() == self.mainFrame().url():
            self.__sslConfiguration = reply.sslConfiguration()
            self.__sslConfiguration.url = QUrl(reply.url())
        
        if reply.error() == QNetworkReply.NoError and \
           mainFrameRequest and \
           reply.url() == self.mainFrame().url():
            modified = reply.header(QNetworkRequest.LastModifiedHeader)
            if modified and modified.isValid():
                import Helpviewer.HelpWindow
                manager = Helpviewer.HelpWindow.HelpWindow.bookmarksManager()
                from .Bookmarks.BookmarkNode import BookmarkNode
                for bookmark in manager.bookmarksForUrl(reply.url()):
                    manager.setTimestamp(bookmark, BookmarkNode.TsModified,
                                         modified)
    
    def getSslCertificate(self):
        """
        Public method to get a reference to the SSL certificate.
        
        @return amended SSL certificate (QSslCertificate)
        """
        if self.__sslConfiguration is None:
            return None
        
        sslInfo = self.__sslConfiguration.peerCertificate()
        sslInfo.url = QUrl(self.__sslConfiguration.url)
        return sslInfo
    
    def getSslCertificateChain(self):
        """
        Public method to get a reference to the SSL certificate chain.
        
        @return SSL certificate chain (list of QSslCertificate)
        """
        if self.__sslConfiguration is None:
            return []
        
        chain = self.__sslConfiguration.peerCertificateChain()
        return chain
    
    def getSslConfiguration(self):
        """
        Public method to return a reference to the current SSL configuration.
        
        @return reference to the SSL configuration in use (QSslConfiguration)
        """
        return self.__sslConfiguration
    
    def showSslInfo(self, pos):
        """
        Public slot to show some SSL information for the loaded page.
        
        @param pos position to show the info at (QPoint)
        """
        if SSL_AVAILABLE and self.__sslConfiguration is not None:
            from E5Network.E5SslInfoWidget import E5SslInfoWidget
            widget = E5SslInfoWidget(
                self.mainFrame().url(), self.__sslConfiguration, self.view())
            widget.showAt(pos)
        else:
            E5MessageBox.warning(
                self.view(),
                self.tr("SSL Info"),
                self.tr("""This site does not contain SSL information."""))
    
    def hasValidSslInfo(self):
        """
        Public method to check, if the page has a valid SSL certificate.
        
        @return flag indicating a valid SSL certificate (boolean)
        """
        if self.__sslConfiguration is None:
            return False
        
        certList = self.__sslConfiguration.peerCertificateChain()
        if not certList:
            return False
        
        certificateDict = Globals.toDict(
            Preferences.Prefs.settings.value("Ssl/CaCertificatesDict"))
        for server in certificateDict:
            localCAList = QSslCertificate.fromData(certificateDict[server])
            for cert in certList:
                if cert in localCAList:
                    return True
        
        if qVersionTuple() >= (5, 0, 0):
            for cert in certList:
                if cert.isBlacklisted():
                    return False
        else:
            for cert in certList:
                if not cert.isValid():
                    return False
        
        return True
    
    @classmethod
    def webPluginFactory(cls):
        """
        Class method to get a reference to the web plug-in factory
        instance.
        
        @return reference to the web plug-in factory instance (WebPluginFactory
        """
        if cls._webPluginFactory is None:
            from .WebPlugins.WebPluginFactory import WebPluginFactory
            cls._webPluginFactory = WebPluginFactory()
        
        return cls._webPluginFactory
    
    def event(self, evt):
        """
        Public method implementing the event handler.
        
        @param evt reference to the event (QEvent)
        @return flag indicating that the event was handled (boolean)
        """
        if evt.type() == QEvent.Leave:
            # Fake a mouse move event just outside of the widget to trigger
            # the WebKit event handler's mouseMoved function. This implements
            # the interesting mouse-out behavior like invalidating scrollbars.
            fakeEvent = QMouseEvent(QEvent.MouseMove, QPoint(0, -1),
                                    Qt.NoButton, Qt.NoButton, Qt.NoModifier)
            return super(HelpWebPage, self).event(fakeEvent)
        
        return super(HelpWebPage, self).event(evt)
    
    def __saveFrameStateRequested(self, frame, itm):
        """
        Private slot to save the page state (i.e. zoom level and scroll
        position).
        
        Note: Code is based on qutebrowser.
        
        @param frame frame to be saved
        @type QWebFrame
        @param itm web history item to be saved
        @type QWebHistoryItem
        """
        try:
            if frame != self.mainFrame():
                return
        except RuntimeError:
            # With Qt 5.2.1 (Ubuntu Trusty) we get this when closing a tab:
            #     RuntimeError: wrapped C/C++ object of type BrowserPage has
            #     been deleted
            # Since the information here isn't that important for closing web
            # views anyways, we ignore this error.
            return
        data = {
            'zoom': frame.zoomFactor(),
            'scrollPos': frame.scrollPosition(),
        }
        itm.setUserData(data)
    
    def __restoreFrameStateRequested(self, frame):
        """
        Private slot to restore scroll position and zoom level from
        history.
        
        Note: Code is based on qutebrowser.
        
        @param frame frame to be restored
        @type QWebFrame
        """
        if frame != self.mainFrame():
            return
        
        data = self.history().currentItem().userData()
        if data is None:
            return
        
        if 'zoom' in data:
            frame.page().view().setZoomValue(int(data['zoom'] * 100),
                                             saveValue=False)
        
        if 'scrollPos' in data and frame.scrollPosition() == QPoint(0, 0):
            frame.setScrollPosition(data['scrollPos'])

###############################################################################


class HelpBrowser(QWebView):
    """
    Class implementing the helpbrowser widget.
    
    This is a subclass of the Qt QWebView to implement an
    interface compatible with the QTextBrowser based variant.
    
    @signal sourceChanged(QUrl) emitted after the current URL has changed
    @signal forwardAvailable(bool) emitted after the current URL has changed
    @signal backwardAvailable(bool) emitted after the current URL has changed
    @signal highlighted(str) emitted, when the mouse hovers over a link
    @signal search(QUrl) emitted, when a search is requested
    @signal zoomValueChanged(int) emitted to signal a change of the zoom value
    """
    sourceChanged = pyqtSignal(QUrl)
    forwardAvailable = pyqtSignal(bool)
    backwardAvailable = pyqtSignal(bool)
    highlighted = pyqtSignal(str)
    search = pyqtSignal(QUrl)
    zoomValueChanged = pyqtSignal(int)
    
    ZoomLevels = [
        30, 50, 67, 80, 90,
        100,
        110, 120, 133, 150, 170, 200, 240, 300,
    ]
    ZoomLevelDefault = 100
    
    def __init__(self, mainWindow, parent=None, name=""):
        """
        Constructor
        
        @param mainWindow reference to the main window (HelpWindow)
        @param parent parent widget of this window (QWidget)
        @param name name of this window (string)
        """
        super(HelpBrowser, self).__init__(parent)
        self.setObjectName(name)
        self.setWhatsThis(self.tr(
            """<b>Help Window</b>"""
            """<p>This window displays the selected help information.</p>"""
        ))
        
        import Helpviewer.HelpWindow
        self.__speedDial = Helpviewer.HelpWindow.HelpWindow.speedDial()
        
        self.__page = HelpWebPage(self)
        self.setPage(self.__page)
        
        self.mw = mainWindow
        self.ctrlPressed = False
        self.__isLoading = False
        self.__progress = 0
        
        self.__currentZoom = 100
        self.__zoomLevels = HelpBrowser.ZoomLevels[:]
        
        self.__javaScriptBinding = None
        self.__javaScriptEricObject = None
        
        self.mw.zoomTextOnlyChanged.connect(self.__applyZoom)
        
        self.page().setLinkDelegationPolicy(QWebPage.DelegateAllLinks)
        self.linkClicked.connect(self.setSource)
        
        self.urlChanged.connect(self.__urlChanged)
        self.statusBarMessage.connect(self.__statusBarMessage)
        self.page().linkHovered.connect(self.__linkHovered)
        
        self.loadStarted.connect(self.__loadStarted)
        self.loadProgress.connect(self.__loadProgress)
        self.loadFinished.connect(self.__loadFinished)
        
        self.page().setForwardUnsupportedContent(True)
        self.page().unsupportedContent.connect(self.__unsupportedContent)
        
        self.page().featurePermissionRequested.connect(
            self.__featurePermissionRequested)
        
        self.page().downloadRequested.connect(self.__downloadRequested)
        self.page().frameCreated.connect(
            lambda frame: self.__addExternalBinding(frame, False))
        self.__addExternalBinding(self.page().mainFrame(), False)
        
        self.page().databaseQuotaExceeded.connect(self.__databaseQuotaExceeded)
        
        self.mw.openSearchManager().currentEngineChanged.connect(
            self.__currentEngineChanged)
        
        self.setAcceptDrops(True)
        
        self.__enableAccessKeys = Preferences.getHelp("AccessKeysEnabled")
        self.__accessKeysPressed = False
        self.__accessKeyLabels = []
        self.__accessKeyNodes = {}
        
        self.page().loadStarted.connect(self.__hideAccessKeys)
        self.page().scrollRequested.connect(self.__hideAccessKeys)
        
        self.__rss = []
        
        self.__clickedFrame = None
        
        self.mw.personalInformationManager().connectPage(self.page())
        self.mw.greaseMonkeyManager().connectPage(self.page())
        
        self.__inspector = None
        
        self.grabGesture(Qt.PinchGesture)
    
    def __addExternalBinding(self, frame, frameCleared):
        """
        Private slot to add javascript bindings for adding search providers.
        
        @param frame reference to the web frame
        @type QWebFrame
        @param frameCleared flag indicate, that the frame was cleared
        @type bool
        """
        self.page().settings().setAttribute(QWebSettings.JavascriptEnabled,
                                            True)
        if self.__javaScriptBinding is None:
            self.__javaScriptBinding = JavaScriptExternalObject(self.mw, self)
        
        if frameCleared:
            # called from QWebFrame.javaScriptWindowObjectCleared
            if isinstance(frame, HelpWebPage):
                frame = frame.mainFrame()
            if frame.url().scheme() == "eric" and frame.url().path() == "home":
                if self.__javaScriptEricObject is None:
                    self.__javaScriptEricObject = JavaScriptEricObject(
                        self.mw, self)
                frame.addToJavaScriptWindowObject(
                    "eric", self.__javaScriptEricObject)
            elif frame.url().scheme() == "eric" and \
                    frame.url().path() == "speeddial":
                frame.addToJavaScriptWindowObject(
                    "speeddial", self.__speedDial)
                self.__speedDial.addWebFrame(frame)
        else:
            # called from QWebPage.frameCreated
            frame.javaScriptWindowObjectCleared.connect(
                lambda: self.__addExternalBinding(frame, True))
        frame.addToJavaScriptWindowObject("external", self.__javaScriptBinding)
    
    def linkedResources(self, relation=""):
        """
        Public method to extract linked resources.
        
        @param relation relation to extract (string)
        @return list of linked resources (list of LinkedResource)
        """
        resources = []
        
        baseUrl = self.page().mainFrame().baseUrl()
        
        linkElements = self.page().mainFrame().findAllElements(
            "html > head > link")
        
        for linkElement in linkElements.toList():
            rel = linkElement.attribute("rel")
            href = linkElement.attribute("href")
            type_ = linkElement.attribute("type")
            title = linkElement.attribute("title")
            
            if href == "" or type_ == "":
                continue
            if relation and rel != relation:
                continue
            
            resource = LinkedResource()
            resource.rel = rel
            resource.type_ = type_
            resource.href = baseUrl.resolved(
                QUrl.fromEncoded(href.encode("utf-8")))
            resource.title = title
            
            resources.append(resource)
        
        return resources
    
    def __currentEngineChanged(self):
        """
        Private slot to track a change of the current search engine.
        """
        if self.url().toString() == "eric:home":
            self.reload()
    
    def setSource(self, name, requestData=None):
        """
        Public method used to set the source to be displayed.
        
        @param name filename to be shown (QUrl)
        @param requestData tuple containing the request data (QNetworkRequest,
            QNetworkAccessManager.Operation, QByteArray)
        """
        if (name is None or not name.isValid()) and requestData is None:
            return
        
        if name is None and requestData is not None:
            name = requestData[0].url()
        
        if self.ctrlPressed:
            # open in a new window
            self.mw.newTab(name)
            self.ctrlPressed = False
            return
        
        if not name.scheme():
            if not os.path.exists(name.toString()):
                name.setScheme(Preferences.getWebBrowser("DefaultScheme"))
            else:
                if Utilities.isWindowsPlatform():
                    name.setUrl("file:///" + Utilities.fromNativeSeparators(
                        name.toString()))
                else:
                    name.setUrl("file://" + name.toString())
        
        if len(name.scheme()) == 1 or \
           name.scheme() == "file":
            # name is a local file
            if name.scheme() and len(name.scheme()) == 1:
                # it is a local path on win os
                name = QUrl.fromLocalFile(name.toString())
            
            if not QFileInfo(name.toLocalFile()).exists():
                E5MessageBox.critical(
                    self,
                    self.tr("eric6 Web Browser"),
                    self.tr(
                        """<p>The file <b>{0}</b> does not exist.</p>""")
                    .format(name.toLocalFile()))
                return

            if name.toLocalFile().endswith(".pdf") or \
               name.toLocalFile().endswith(".PDF") or \
               name.toLocalFile().endswith(".chm") or \
               name.toLocalFile().endswith(".CHM"):
                started = QDesktopServices.openUrl(name)
                if not started:
                    E5MessageBox.critical(
                        self,
                        self.tr("eric6 Web Browser"),
                        self.tr(
                            """<p>Could not start a viewer"""
                            """ for file <b>{0}</b>.</p>""")
                        .format(name.path()))
                return
        elif name.scheme() in ["mailto"]:
            started = QDesktopServices.openUrl(name)
            if not started:
                E5MessageBox.critical(
                    self,
                    self.tr("eric6 Web Browser"),
                    self.tr(
                        """<p>Could not start an application"""
                        """ for URL <b>{0}</b>.</p>""")
                    .format(name.toString()))
            return
        elif name.scheme() == "javascript":
            scriptSource = QUrl.fromPercentEncoding(name.toString(
                QUrl.FormattingOptions(QUrl.TolerantMode | QUrl.RemoveScheme)))
            self.page().mainFrame().evaluateJavaScript(scriptSource)
            return
        else:
            if name.toString().endswith(".pdf") or \
               name.toString().endswith(".PDF") or \
               name.toString().endswith(".chm") or \
               name.toString().endswith(".CHM"):
                started = QDesktopServices.openUrl(name)
                if not started:
                    E5MessageBox.critical(
                        self,
                        self.tr("eric6 Web Browser"),
                        self.tr(
                            """<p>Could not start a viewer"""
                            """ for file <b>{0}</b>.</p>""")
                        .format(name.path()))
                return
        
        if requestData is not None:
            self.load(*requestData)
        else:
            self.load(name)

    def source(self):
        """
        Public method to return the URL of the loaded page.
        
        @return URL loaded in the help browser (QUrl)
        """
        return self.url()
    
    def documentTitle(self):
        """
        Public method to return the title of the loaded page.
        
        @return title (string)
        """
        return self.title()
    
    def backward(self):
        """
        Public slot to move backwards in history.
        """
        self.triggerPageAction(QWebPage.Back)
        self.__urlChanged(self.history().currentItem().url())
    
    def forward(self):
        """
        Public slot to move forward in history.
        """
        self.triggerPageAction(QWebPage.Forward)
        self.__urlChanged(self.history().currentItem().url())
    
    def home(self):
        """
        Public slot to move to the first page loaded.
        """
        homeUrl = QUrl(Preferences.getHelp("HomePage"))
        self.setSource(homeUrl)
        self.__urlChanged(self.history().currentItem().url())
    
    def reload(self):
        """
        Public slot to reload the current page.
        """
        self.triggerPageAction(QWebPage.Reload)
    
    def copy(self):
        """
        Public slot to copy the selected text.
        """
        self.triggerPageAction(QWebPage.Copy)
    
    def isForwardAvailable(self):
        """
        Public method to determine, if a forward move in history is possible.
        
        @return flag indicating move forward is possible (boolean)
        """
        return self.history().canGoForward()
    
    def isBackwardAvailable(self):
        """
        Public method to determine, if a backwards move in history is possible.
        
        @return flag indicating move backwards is possible (boolean)
        """
        return self.history().canGoBack()
    
    def __levelForZoom(self, zoom):
        """
        Private method determining the zoom level index given a zoom factor.
        
        @param zoom zoom factor (integer)
        @return index of zoom factor (integer)
        """
        try:
            index = self.__zoomLevels.index(zoom)
        except ValueError:
            for index in range(len(self.__zoomLevels)):
                if zoom <= self.__zoomLevels[index]:
                    break
        return index
    
    def __applyZoom(self):
        """
        Private slot to apply the current zoom factor.
        """
        self.setZoomValue(self.__currentZoom)
    
    def setZoomValue(self, value, saveValue=True):
        """
        Public method to set the zoom value.
        
        @param value zoom value (integer)
        @keyparam saveValue flag indicating to save the zoom value with the
            zoom manager
        @type bool
        """
        if value != self.zoomValue():
            try:
                self.setZoomFactor(value / 100.0)
            except AttributeError:
                self.setTextSizeMultiplier(value / 100.0)
            self.__currentZoom = value
            if saveValue:
                Helpviewer.HelpWindow.HelpWindow.zoomManager().setZoomValue(
                    self.url(), value)
            self.zoomValueChanged.emit(value)
    
    def zoomValue(self):
        """
        Public method to get the current zoom value.
        
        @return zoom value (integer)
        """
        try:
            val = self.zoomFactor() * 100
        except AttributeError:
            val = self.textSizeMultiplier() * 100
        return int(val)
    
    def zoomIn(self):
        """
        Public slot to zoom into the page.
        """
        index = self.__levelForZoom(self.__currentZoom)
        if index < len(self.__zoomLevels) - 1:
            self.__currentZoom = self.__zoomLevels[index + 1]
        self.__applyZoom()
    
    def zoomOut(self):
        """
        Public slot to zoom out of the page.
        """
        index = self.__levelForZoom(self.__currentZoom)
        if index > 0:
            self.__currentZoom = self.__zoomLevels[index - 1]
        self.__applyZoom()
    
    def zoomReset(self):
        """
        Public method to reset the zoom factor.
        """
        index = self.__levelForZoom(HelpBrowser.ZoomLevelDefault)
        self.__currentZoom = self.__zoomLevels[index]
        self.__applyZoom()
    
    def hasSelection(self):
        """
        Public method to determine, if there is some text selected.
        
        @return flag indicating text has been selected (boolean)
        """
        return self.selectedText() != ""
    
    def findNextPrev(self, txt, case, backwards, wrap, highlightAll):
        """
        Public slot to find the next occurrence of a text.
        
        @param txt text to search for (string)
        @param case flag indicating a case sensitive search (boolean)
        @param backwards flag indicating a backwards search (boolean)
        @param wrap flag indicating to wrap around (boolean)
        @param highlightAll flag indicating to highlight all occurrences
            (boolean)
        @return flag indicating that a match was found (boolean)
        """
        findFlags = QWebPage.FindFlags()
        if case:
            findFlags |= QWebPage.FindCaseSensitively
        if backwards:
            findFlags |= QWebPage.FindBackward
        if wrap:
            findFlags |= QWebPage.FindWrapsAroundDocument
        try:
            if highlightAll:
                findFlags |= QWebPage.HighlightAllOccurrences
        except AttributeError:
            pass
        
        return self.findText(txt, findFlags)
    
    def __isMediaElement(self, element):
        """
        Private method to check, if the given element is a media element.
        
        @param element element to be checked (QWebElement)
        @return flag indicating a media element (boolean)
        """
        return element.tagName().lower() in ["video", "audio"]
    
    def contextMenuEvent(self, evt):
        """
        Protected method called to create a context menu.
        
        This method is overridden from QWebView.
        
        @param evt reference to the context menu event object
            (QContextMenuEvent)
        """
        from .UserAgent.UserAgentMenu import UserAgentMenu
        menu = QMenu(self)
        
        if self.url().toString() == "eric:speeddial":
            # special menu for the spedd dial page
            menu.addAction(self.mw.newTabAct)
            menu.addAction(self.mw.newAct)
            menu.addSeparator()
            menu.addAction(self.mw.backAct)
            menu.addAction(self.mw.forwardAct)
            menu.addSeparator()
            menu.addAction(
                UI.PixmapCache.getIcon("plus.png"),
                self.tr("Add New Page"), self.__addSpeedDial)
            menu.addAction(
                UI.PixmapCache.getIcon("preferences-general.png"),
                self.tr("Configure Speed Dial"), self.__configureSpeedDial)
            menu.addSeparator()
            menu.addAction(
                UI.PixmapCache.getIcon("reload.png"),
                self.tr("Reload All Dials"), self.__reloadAllSpeedDials)
            menu.addSeparator()
            menu.addAction(
                self.tr("Reset to Default Dials"), self.__resetSpeedDials)
            
            menu.exec_(evt.globalPos())
            return
        
        frameAtPos = self.page().frameAt(evt.pos())
        hit = self.page().mainFrame().hitTestContent(evt.pos())
        if not hit.linkUrl().isEmpty():
            act = menu.addAction(
                UI.PixmapCache.getIcon("openNewTab.png"),
                self.tr("Open Link in New Tab\tCtrl+LMB"))
            act.setData(hit.linkUrl())
            act.triggered.connect(
                lambda: self.__openLinkInNewTab(act))
            menu.addSeparator()
            menu.addAction(
                UI.PixmapCache.getIcon("download.png"),
                self.tr("Save Lin&k"), self.__downloadLink)
            act = menu.addAction(
                UI.PixmapCache.getIcon("bookmark22.png"),
                self.tr("Bookmark this Link"))
            act.setData(hit.linkUrl())
            act.triggered.connect(
                lambda: self.__bookmarkLink(act))
            menu.addSeparator()
            menu.addAction(
                UI.PixmapCache.getIcon("editCopy.png"),
                self.tr("Copy Link to Clipboard"), self.__copyLink)
            act = menu.addAction(
                UI.PixmapCache.getIcon("mailSend.png"),
                self.tr("Send Link"))
            act.setData(hit.linkUrl())
            act.triggered.connect(
                lambda: self.__sendLink(act))
            if Preferences.getHelp("VirusTotalEnabled") and \
               Preferences.getHelp("VirusTotalServiceKey") != "":
                act = menu.addAction(
                    UI.PixmapCache.getIcon("virustotal.png"),
                    self.tr("Scan Link with VirusTotal"))
                act.setData(hit.linkUrl())
                act.triggered.connect(
                    lambda: self.__virusTotal(act))
        
        if not hit.imageUrl().isEmpty():
            if not menu.isEmpty():
                menu.addSeparator()
            act = menu.addAction(
                UI.PixmapCache.getIcon("openNewTab.png"),
                self.tr("Open Image in New Tab"))
            act.setData(hit.imageUrl())
            act.triggered.connect(
                lambda: self.__openLinkInNewTab(act))
            menu.addSeparator()
            menu.addAction(
                UI.PixmapCache.getIcon("download.png"),
                self.tr("Save Image"), self.__downloadImage)
            menu.addAction(
                self.tr("Copy Image to Clipboard"), self.__copyImage)
            act = menu.addAction(
                UI.PixmapCache.getIcon("editCopy.png"),
                self.tr("Copy Image Location to Clipboard"))
            act.setData(hit.imageUrl().toString())
            act.triggered.connect(
                lambda: self.__copyLocation(act))
            act = menu.addAction(
                UI.PixmapCache.getIcon("mailSend.png"),
                self.tr("Send Image Link"))
            act.setData(hit.imageUrl())
            act.triggered.connect(
                lambda: self.__sendLink(act))
            menu.addSeparator()
            act = menu.addAction(
                UI.PixmapCache.getIcon("adBlockPlus.png"),
                self.tr("Block Image"))
            act.setData(hit.imageUrl().toString())
            act.triggered.connect(
                lambda: self.__blockImage(act))
            if Preferences.getHelp("VirusTotalEnabled") and \
               Preferences.getHelp("VirusTotalServiceKey") != "":
                act = menu.addAction(
                    UI.PixmapCache.getIcon("virustotal.png"),
                    self.tr("Scan Image with VirusTotal"))
                act.setData(hit.imageUrl())
                act.triggered.connect(
                    lambda: self.__virusTotal(act))
        
        element = hit.element()
        if not element.isNull():
            if self.__isMediaElement(element):
                if not menu.isEmpty():
                    menu.addSeparator()
                
                self.__clickedMediaElement = element
                
                paused = element.evaluateJavaScript("this.paused")
                muted = element.evaluateJavaScript("this.muted")
                videoUrl = QUrl(element.evaluateJavaScript("this.currentSrc"))
                
                if paused:
                    menu.addAction(
                        UI.PixmapCache.getIcon("mediaPlaybackStart.png"),
                        self.tr("Play"), self.__pauseMedia)
                else:
                    menu.addAction(
                        UI.PixmapCache.getIcon("mediaPlaybackPause.png"),
                        self.tr("Pause"), self.__pauseMedia)
                if muted:
                    menu.addAction(
                        UI.PixmapCache.getIcon("audioVolumeHigh.png"),
                        self.tr("Unmute"), self.__muteMedia)
                else:
                    menu.addAction(
                        UI.PixmapCache.getIcon("audioVolumeMuted.png"),
                        self.tr("Mute"), self.__muteMedia)
                menu.addSeparator()
                act = menu.addAction(
                    UI.PixmapCache.getIcon("editCopy.png"),
                    self.tr("Copy Media Address to Clipboard"))
                act.setData(videoUrl.toString())
                act.triggered.connect(
                    lambda: self.__copyLocation(act))
                act = menu.addAction(
                    UI.PixmapCache.getIcon("mailSend.png"),
                    self.tr("Send Media Address"))
                act.setData(videoUrl)
                act.triggered.connect(
                    lambda: self.__sendLink(act))
                act = menu.addAction(
                    UI.PixmapCache.getIcon("download.png"),
                    self.tr("Save Media"))
                act.setData(videoUrl)
                act.triggered.connect(
                    lambda: self.__downloadMedia(act))
            
            if element.tagName().lower() in ["input", "textarea"]:
                if menu.isEmpty():
                    pageMenu = self.page().createStandardContextMenu()
                    directionFound = False
                    # used to detect double direction entry
                    for act in pageMenu.actions():
                        if act.isSeparator():
                            menu.addSeparator()
                            continue
                        if act.menu():
                            if self.pageAction(
                                    QWebPage.SetTextDirectionDefault) in \
                                    act.menu().actions():
                                if directionFound:
                                    act.setVisible(False)
                                directionFound = True
                            elif self.pageAction(QWebPage.ToggleBold) in \
                                    act.menu().actions():
                                act.setVisible(False)
                        elif act == self.pageAction(QWebPage.InspectElement):
                            # we have our own inspect entry
                            act.setVisible(False)
                        menu.addAction(act)
                    pageMenu = None
        
        if not menu.isEmpty():
            menu.addSeparator()
        
        self.mw.personalInformationManager().createSubMenu(menu, self, hit)
        
        menu.addAction(self.mw.newTabAct)
        menu.addAction(self.mw.newAct)
        menu.addSeparator()
        menu.addAction(self.mw.saveAsAct)
        menu.addSeparator()
        
        if frameAtPos and self.page().mainFrame() != frameAtPos:
            self.__clickedFrame = frameAtPos
            fmenu = QMenu(self.tr("This Frame"))
            frameUrl = self.__clickedFrame.url()
            if frameUrl.isValid():
                fmenu.addAction(
                    self.tr("Show &only this frame"),
                    self.__loadClickedFrame)
                act = fmenu.addAction(
                    UI.PixmapCache.getIcon("openNewTab.png"),
                    self.tr("Show in new &tab"))
                act.setData(self.__clickedFrame.url())
                act.triggered.connect(
                    lambda: self.__openLinkInNewTab(act))
                fmenu.addSeparator()
            fmenu.addAction(
                UI.PixmapCache.getIcon("print.png"),
                self.tr("&Print"), self.__printClickedFrame)
            fmenu.addAction(
                UI.PixmapCache.getIcon("printPreview.png"),
                self.tr("Print Preview"), self.__printPreviewClickedFrame)
            fmenu.addAction(
                UI.PixmapCache.getIcon("printPdf.png"),
                self.tr("Print as PDF"), self.__printPdfClickedFrame)
            fmenu.addSeparator()
            fmenu.addAction(
                UI.PixmapCache.getIcon("zoomIn.png"),
                self.tr("Zoom &in"), self.__zoomInClickedFrame)
            fmenu.addAction(
                UI.PixmapCache.getIcon("zoomReset.png"),
                self.tr("Zoom &reset"), self.__zoomResetClickedFrame)
            fmenu.addAction(
                UI.PixmapCache.getIcon("zoomOut.png"),
                self.tr("Zoom &out"), self.__zoomOutClickedFrame)
            fmenu.addSeparator()
            fmenu.addAction(
                self.tr("Show frame so&urce"),
                self.__showClickedFrameSource)
            
            menu.addMenu(fmenu)
            menu.addSeparator()
        
        menu.addAction(
            UI.PixmapCache.getIcon("bookmark22.png"),
            self.tr("Bookmark this Page"), self.addBookmark)
        act = menu.addAction(
            UI.PixmapCache.getIcon("mailSend.png"),
            self.tr("Send Page Link"))
        act.setData(self.url())
        act.triggered.connect(
            lambda: self.__sendLink(act))
        menu.addSeparator()
        self.__userAgentMenu = UserAgentMenu(self.tr("User Agent"),
                                             url=self.url())
        menu.addMenu(self.__userAgentMenu)
        menu.addSeparator()
        menu.addAction(self.mw.backAct)
        menu.addAction(self.mw.forwardAct)
        menu.addAction(self.mw.homeAct)
        menu.addSeparator()
        menu.addAction(self.mw.zoomInAct)
        menu.addAction(self.mw.zoomResetAct)
        menu.addAction(self.mw.zoomOutAct)
        menu.addSeparator()
        if self.selectedText():
            menu.addAction(self.mw.copyAct)
            act = menu.addAction(
                UI.PixmapCache.getIcon("mailSend.png"),
                self.tr("Send Text"))
            act.setData(self.selectedText())
            act.triggered.connect(
                lambda: self.__sendLink(act))
        menu.addAction(self.mw.findAct)
        menu.addSeparator()
        if self.selectedText():
            self.__searchMenu = menu.addMenu(self.tr("Search with..."))
            
            from .OpenSearch.OpenSearchEngineAction import \
                OpenSearchEngineAction
            engineNames = self.mw.openSearchManager().allEnginesNames()
            for engineName in engineNames:
                engine = self.mw.openSearchManager().engine(engineName)
                act = OpenSearchEngineAction(engine, self.__searchMenu)
                act.setData(engineName)
                self.__searchMenu.addAction(act)
            self.__searchMenu.triggered.connect(self.__searchRequested)
            
            menu.addSeparator()
            
            from .HelpLanguagesDialog import HelpLanguagesDialog
            languages = Preferences.toList(
                Preferences.Prefs.settings.value(
                    "Help/AcceptLanguages",
                    HelpLanguagesDialog.defaultAcceptLanguages()))
            if languages:
                language = languages[0]
                langCode = language.split("[")[1][:2]
                googleTranslatorUrl = QUrl(
                    "http://translate.google.com/#auto|{0}|{1}".format(
                        langCode, self.selectedText()))
                act = menu.addAction(
                    UI.PixmapCache.getIcon("translate.png"),
                    self.tr("Google Translate"))
                act.setData(googleTranslatorUrl)
                act.triggered.connect(
                    lambda: self.__openLinkInNewTab(act))
                wiktionaryUrl = QUrl(
                    "http://{0}.wiktionary.org/wiki/Special:Search?search={1}"
                    .format(langCode, self.selectedText()))
                act = menu.addAction(
                    UI.PixmapCache.getIcon("wikipedia.png"),
                    self.tr("Dictionary"))
                act.setData(wiktionaryUrl)
                act.triggered.connect(
                    lambda: self.__openLinkInNewTab(act))
                menu.addSeparator()
            
            guessedUrl = QUrl.fromUserInput(self.selectedText().strip())
            if self.__isUrlValid(guessedUrl):
                act = menu.addAction(self.tr("Go to web address"))
                act.setData(guessedUrl)
                act.triggered.connect(
                    lambda: self.__openLinkInNewTab(act))
                menu.addSeparator()
        
        element = hit.element()
        if not element.isNull() and \
           element.tagName().lower() == "input" and \
           element.attribute("type", "text") == "text":
            act = menu.addAction(
                self.tr("Add to web search toolbar"))
            act.setData(element)
            act.triggered.connect(
                lambda: self.__addSearchEngine(act))
            menu.addSeparator()
        
        menu.addAction(
            UI.PixmapCache.getIcon("webInspector.png"),
            self.tr("Web Inspector..."), self.__webInspector)
        
        menu.exec_(evt.globalPos())
    
    def __isUrlValid(self, url):
        """
        Private method to check a URL for validity.
        
        @param url URL to be checked (QUrl)
        @return flag indicating a valid URL (boolean)
        """
        return url.isValid() and \
            bool(url.host()) and \
            bool(url.scheme()) and \
            "." in url.host()
    
    def __openLinkInNewTab(self, act):
        """
        Private method called by the context menu to open a link in a new
        window.
        
        @param act reference to the action that triggered
        @type QAction
        """
        url = act.data()
        if url.isEmpty():
            return
        
        self.ctrlPressed = True
        self.setSource(url)
        self.ctrlPressed = False
    
    def __bookmarkLink(self, act):
        """
        Private slot to bookmark a link via the context menu.
        
        @param act reference to the action that triggered
        @type QAction
        """
        url = act.data()
        if url.isEmpty():
            return
        
        from .Bookmarks.AddBookmarkDialog import AddBookmarkDialog
        dlg = AddBookmarkDialog()
        dlg.setUrl(bytes(url.toEncoded()).decode())
        dlg.exec_()
    
    def __sendLink(self, act):
        """
        Private slot to send a link via email.
        
        @param act reference to the action that triggered
        @type QAction
        """
        data = act.data()
        if isinstance(data, QUrl) and data.isEmpty():
            return
        
        if isinstance(data, QUrl):
            data = data.toString()
        QDesktopServices.openUrl(QUrl("mailto:?body=" + data))
    
    def __downloadLink(self):
        """
        Private slot to download a link and save it to disk.
        """
        self.pageAction(QWebPage.DownloadLinkToDisk).trigger()
    
    def __copyLink(self):
        """
        Private slot to copy a link to the clipboard.
        """
        self.pageAction(QWebPage.CopyLinkToClipboard).trigger()
    
    def __downloadImage(self):
        """
        Private slot to download an image and save it to disk.
        """
        self.pageAction(QWebPage.DownloadImageToDisk).trigger()
    
    def __copyImage(self):
        """
        Private slot to copy an image to the clipboard.
        """
        self.pageAction(QWebPage.CopyImageToClipboard).trigger()
    
    def __copyLocation(self, act):
        """
        Private slot to copy an image or media location to the clipboard.
        
        @param act reference to the action that triggered
        @type QAction
        """
        url = act.data()
        QApplication.clipboard().setText(url)
    
    def __blockImage(self, act):
        """
        Private slot to add a block rule for an image URL.
        
        @param act reference to the action that triggered
        @type QAction
        """
        import Helpviewer.HelpWindow
        url = act.data()
        dlg = Helpviewer.HelpWindow.HelpWindow.adBlockManager().showDialog()
        dlg.addCustomRule(url)
    
    def __downloadMedia(self, act):
        """
        Private slot to download a media and save it to disk.
        
        @param act reference to the action that triggered
        @type QAction
        """
        url = act.data()
        self.mw.downloadManager().download(url, True, mainWindow=self.mw)
    
    def __pauseMedia(self):
        """
        Private slot to pause or play the selected media.
        """
        paused = self.__clickedMediaElement.evaluateJavaScript("this.paused")
        
        if paused:
            self.__clickedMediaElement.evaluateJavaScript("this.play()")
        else:
            self.__clickedMediaElement.evaluateJavaScript("this.pause()")
    
    def __muteMedia(self):
        """
        Private slot to (un)mute the selected media.
        """
        muted = self.__clickedMediaElement.evaluateJavaScript("this.muted")
        
        if muted:
            self.__clickedMediaElement.evaluateJavaScript("this.muted = false")
        else:
            self.__clickedMediaElement.evaluateJavaScript("this.muted = true")
    
    def __virusTotal(self, act):
        """
        Private slot to scan the selected URL with VirusTotal.
        
        @param act reference to the action that triggered
        @type QAction
        """
        url = act.data()
        self.mw.requestVirusTotalScan(url)
    
    def __searchRequested(self, act):
        """
        Private slot to search for some text with a selected search engine.
        
        @param act reference to the action that triggered this slot (QAction)
        """
        searchText = self.selectedText()
        
        if not searchText:
            return
        
        engineName = act.data()
        if engineName:
            engine = self.mw.openSearchManager().engine(engineName)
            self.search.emit(engine.searchUrl(searchText))
    
    def __addSearchEngine(self, act):
        """
        Private slot to add a new search engine.
        
        @param act reference to the action that triggered
        @type QAction
        """
        element = act.data()
        elementName = element.attribute("name")
        formElement = QWebElement(element)
        while formElement.tagName().lower() != "form":
            formElement = formElement.parent()
        
        if formElement.isNull() or \
           formElement.attribute("action") == "":
            return
        
        method = formElement.attribute("method", "get").lower()
        if method != "get":
            E5MessageBox.warning(
                self,
                self.tr("Method not supported"),
                self.tr(
                    """{0} method is not supported.""").format(method.upper()))
            return
        
        searchUrl = QUrl(self.page().mainFrame().baseUrl().resolved(
            QUrl(formElement.attribute("action"))))
        
        if qVersionTuple() >= (5, 0, 0):
            from PyQt5.QtCore import QUrlQuery
            searchUrlQuery = QUrlQuery(searchUrl)
        searchEngines = {}
        inputFields = formElement.findAll("input")
        for inputField in inputFields.toList():
            type_ = inputField.attribute("type", "text")
            name = inputField.attribute("name")
            value = inputField.evaluateJavaScript("this.value")
            
            if type_ == "submit":
                searchEngines[value] = name
            elif type_ == "text":
                if inputField == element:
                    value = "{searchTerms}"
                if qVersionTuple() >= (5, 0, 0):
                    searchUrlQuery.addQueryItem(name, value)
                else:
                    searchUrl.addQueryItem(name, value)
            elif type_ == "checkbox" or type_ == "radio":
                if inputField.evaluateJavaScript("this.checked"):
                    if qVersionTuple() >= (5, 0, 0):
                        searchUrlQuery.addQueryItem(name, value)
                    else:
                        searchUrl.addQueryItem(name, value)
            elif type_ == "hidden":
                if qVersionTuple() >= (5, 0, 0):
                    searchUrlQuery.addQueryItem(name, value)
                else:
                    searchUrl.addQueryItem(name, value)
        
        selectFields = formElement.findAll("select")
        for selectField in selectFields.toList():
            name = selectField.attribute("name")
            selectedIndex = selectField.evaluateJavaScript(
                "this.selectedIndex")
            if selectedIndex == -1:
                continue
            
            options = selectField.findAll("option")
            value = options.at(selectedIndex).toPlainText()
            if qVersionTuple() >= (5, 0, 0):
                searchUrlQuery.addQueryItem(name, value)
            else:
                searchUrl.addQueryItem(name, value)
        
        ok = True
        if len(searchEngines) > 1:
            searchEngine, ok = QInputDialog.getItem(
                self,
                self.tr("Search engine"),
                self.tr("Choose the desired search engine"),
                sorted(searchEngines.keys()), 0, False)
            
            if not ok:
                return
            
            if searchEngines[searchEngine] != "":
                if qVersionTuple() >= (5, 0, 0):
                    searchUrlQuery.addQueryItem(
                        searchEngines[searchEngine], searchEngine)
                else:
                    searchUrl.addQueryItem(
                        searchEngines[searchEngine], searchEngine)
        engineName = ""
        labels = formElement.findAll('label[for="{0}"]'.format(elementName))
        if labels.count() > 0:
            engineName = labels.at(0).toPlainText()
        
        engineName, ok = QInputDialog.getText(
            self,
            self.tr("Engine name"),
            self.tr("Enter a name for the engine"),
            QLineEdit.Normal,
            engineName)
        if not ok:
            return
        
        if qVersionTuple() >= (5, 0, 0):
            searchUrl.setQuery(searchUrlQuery)
        
        from .OpenSearch.OpenSearchEngine import OpenSearchEngine
        engine = OpenSearchEngine()
        engine.setName(engineName)
        engine.setDescription(engineName)
        if qVersionTuple() >= (5, 0, 0):
            engine.setSearchUrlTemplate(
                searchUrl.toDisplayString(QUrl.FullyDecoded))
        else:
            engine.setSearchUrlTemplate(searchUrl.toString())
        engine.setImage(self.icon().pixmap(16, 16).toImage())
        
        self.mw.openSearchManager().addEngine(engine)
    
    def __webInspector(self):
        """
        Private slot to show the web inspector window.
        """
        if self.__inspector is None:
            from .HelpInspector import HelpInspector
            self.__inspector = HelpInspector()
            self.__inspector.setPage(self.page())
            self.__inspector.show()
        elif self.__inspector.isVisible():
            self.__inspector.hide()
        else:
            self.__inspector.show()
    
    def closeWebInspector(self):
        """
        Public slot to close the web inspector.
        """
        if self.__inspector is not None:
            if self.__inspector.isVisible():
                self.__inspector.hide()
            self.__inspector.deleteLater()
            self.__inspector = None
    
    def addBookmark(self):
        """
        Public slot to bookmark the current page.
        """
        from .Bookmarks.AddBookmarkDialog import AddBookmarkDialog
        dlg = AddBookmarkDialog()
        dlg.setUrl(bytes(self.url().toEncoded()).decode())
        dlg.setTitle(self.title())
        meta = self.page().mainFrame().metaData()
        if "description" in meta:
            dlg.setDescription(meta["description"][0])
        dlg.exec_()
    
    def dragEnterEvent(self, evt):
        """
        Protected method called by a drag enter event.
        
        @param evt reference to the drag enter event (QDragEnterEvent)
        """
        evt.acceptProposedAction()
    
    def dragMoveEvent(self, evt):
        """
        Protected method called by a drag move event.
        
        @param evt reference to the drag move event (QDragMoveEvent)
        """
        evt.ignore()
        if evt.source() != self:
            if len(evt.mimeData().urls()) > 0:
                evt.acceptProposedAction()
            else:
                url = QUrl(evt.mimeData().text())
                if url.isValid():
                    evt.acceptProposedAction()
        
        if not evt.isAccepted():
            super(HelpBrowser, self).dragMoveEvent(evt)
    
    def dropEvent(self, evt):
        """
        Protected method called by a drop event.
        
        @param evt reference to the drop event (QDropEvent)
        """
        super(HelpBrowser, self).dropEvent(evt)
        if not evt.isAccepted() and \
           evt.source() != self and \
           evt.possibleActions() & Qt.CopyAction:
            url = QUrl()
            if len(evt.mimeData().urls()) > 0:
                url = evt.mimeData().urls()[0]
            if not url.isValid():
                url = QUrl(evt.mimeData().text())
            if url.isValid():
                self.setSource(url)
                evt.acceptProposedAction()
    
    def mousePressEvent(self, evt):
        """
        Protected method called by a mouse press event.
        
        @param evt reference to the mouse event (QMouseEvent)
        """
        self.mw.setEventMouseButtons(evt.buttons())
        self.mw.setEventKeyboardModifiers(evt.modifiers())
        
        if evt.button() == Qt.XButton1:
            self.pageAction(QWebPage.Back).trigger()
        elif evt.button() == Qt.XButton2:
            self.pageAction(QWebPage.Forward).trigger()
        else:
            super(HelpBrowser, self).mousePressEvent(evt)
    
    def mouseReleaseEvent(self, evt):
        """
        Protected method called by a mouse release event.
        
        @param evt reference to the mouse event (QMouseEvent)
        """
        accepted = evt.isAccepted()
        self.__page.event(evt)
        if not evt.isAccepted() and \
           self.mw.eventMouseButtons() & Qt.MidButton:
            url = QUrl(QApplication.clipboard().text(QClipboard.Selection))
            if not url.isEmpty() and \
               url.isValid() and \
               url.scheme() != "":
                self.mw.setEventMouseButtons(Qt.NoButton)
                self.mw.setEventKeyboardModifiers(Qt.NoModifier)
                self.setSource(url)
        evt.setAccepted(accepted)
    
    def wheelEvent(self, evt):
        """
        Protected method to handle wheel events.
        
        @param evt reference to the wheel event (QWheelEvent)
        """
        if qVersionTuple() >= (5, 0, 0):
            delta = evt.angleDelta().y()
        else:
            delta = evt.delta()
        if evt.modifiers() & Qt.ControlModifier:
            if delta < 0:
                self.zoomOut()
            elif delta > 0:
                self.zoomIn()
            evt.accept()
            return
        
        if evt.modifiers() & Qt.ShiftModifier:
            if delta < 0:
                self.backward()
            elif delta > 0:
                self.forward()
            evt.accept()
            return
        
        super(HelpBrowser, self).wheelEvent(evt)
    
    def keyPressEvent(self, evt):
        """
        Protected method called by a key press.
        
        @param evt reference to the key event (QKeyEvent)
        """
        if self.mw.personalInformationManager().viewKeyPressEvent(self, evt):
            return
        
        if self.__enableAccessKeys:
            self.__accessKeysPressed = (
                evt.modifiers() == Qt.ControlModifier and
                evt.key() == Qt.Key_Control)
            if not self.__accessKeysPressed:
                if self.__checkForAccessKey(evt):
                    self.__hideAccessKeys()
                    evt.accept()
                    return
                self.__hideAccessKeys()
            else:
                QTimer.singleShot(300, self.__accessKeyShortcut)
        
        self.ctrlPressed = (evt.key() == Qt.Key_Control)
        super(HelpBrowser, self).keyPressEvent(evt)
    
    def keyReleaseEvent(self, evt):
        """
        Protected method called by a key release.
        
        @param evt reference to the key event (QKeyEvent)
        """
        if self.__enableAccessKeys:
            self.__accessKeysPressed = evt.key() == Qt.Key_Control
        
        self.ctrlPressed = False
        super(HelpBrowser, self).keyReleaseEvent(evt)
    
    def focusOutEvent(self, evt):
        """
        Protected method called by a focus out event.
        
        @param evt reference to the focus event (QFocusEvent)
        """
        if self.__accessKeysPressed:
            self.__hideAccessKeys()
            self.__accessKeysPressed = False
        
        super(HelpBrowser, self).focusOutEvent(evt)
    
    def event(self, evt):
        """
        Public method handling events.
        
        @param evt reference to the event (QEvent)
        @return flag indicating, if the event was handled (boolean)
        """
        if evt.type() == QEvent.Gesture:
            self.gestureEvent(evt)
            return True
        
        return super(HelpBrowser, self).event(evt)
    
    def gestureEvent(self, evt):
        """
        Protected method handling gesture events.
        
        @param evt reference to the gesture event (QGestureEvent
        """
        pinch = evt.gesture(Qt.PinchGesture)
        if pinch:
            if pinch.state() == Qt.GestureStarted:
                pinch.setTotalScaleFactor(self.__currentZoom / 100.0)
            elif pinch.state() == Qt.GestureUpdated:
                scaleFactor = pinch.totalScaleFactor()
                self.__currentZoom = int(scaleFactor * 100)
                self.__applyZoom()
            evt.accept()
    
    def clearHistory(self):
        """
        Public slot to clear the history.
        """
        self.history().clear()
        self.__urlChanged(self.history().currentItem().url())
    
    ###########################################################################
    ## Signal converters below
    ###########################################################################
    
    def __urlChanged(self, url):
        """
        Private slot to handle the urlChanged signal.
        
        @param url the new url (QUrl)
        """
        self.sourceChanged.emit(url)
        
        self.forwardAvailable.emit(self.isForwardAvailable())
        self.backwardAvailable.emit(self.isBackwardAvailable())
    
    def __statusBarMessage(self, text):
        """
        Private slot to handle the statusBarMessage signal.
        
        @param text text to be shown in the status bar (string)
        """
        self.mw.statusBar().showMessage(text)
    
    def __linkHovered(self, link, title, textContent):
        """
        Private slot to handle the linkHovered signal.
        
        @param link the URL of the link (string)
        @param title the link title (string)
        @param textContent text content of the link (string)
        """
        self.highlighted.emit(link)
    
    ###########################################################################
    ## Signal handlers below
    ###########################################################################
    
    def __loadStarted(self):
        """
        Private method to handle the loadStarted signal.
        """
        self.__isLoading = True
        self.__progress = 0
    
    def __loadProgress(self, progress):
        """
        Private method to handle the loadProgress signal.
        
        @param progress progress value (integer)
        """
        self.__progress = progress
    
    def __loadFinished(self, ok):
        """
        Private method to handle the loadFinished signal.
        
        @param ok flag indicating the result (boolean)
        """
        self.__isLoading = False
        self.__progress = 0
        
        if Preferences.getHelp("ClickToFlashEnabled"):
            # this is a hack to make the ClickToFlash button appear
            self.zoomIn()
            self.zoomOut()
        
        zoomValue = Helpviewer.HelpWindow.HelpWindow.zoomManager()\
            .zoomValue(self.url())
        self.setZoomValue(zoomValue)
        
        if ok:
            self.mw.adBlockManager().page().hideBlockedPageEntries(self.page())
            self.mw.passwordManager().fill(self.page())
    
    def isLoading(self):
        """
        Public method to get the loading state.
        
        @return flag indicating the loading state (boolean)
        """
        return self.__isLoading
    
    def progress(self):
        """
        Public method to get the load progress.
        
        @return load progress (integer)
        """
        return self.__progress
    
    def saveAs(self):
        """
        Public method to save the current page to a file.
        """
        url = self.url()
        if url.isEmpty():
            return
        
        self.mw.downloadManager().download(url, True, mainWindow=self.mw)
    
    def __unsupportedContent(self, reply, requestFilename=None,
                             download=False):
        """
        Private slot to handle the unsupportedContent signal.
        
        @param reply reference to the reply object (QNetworkReply)
        @keyparam requestFilename indicating to ask for a filename
            (boolean or None). If it is None, the behavior is determined
            by a configuration option.
        @keyparam download flag indicating a download operation (boolean)
        """
        if reply is None:
            return
        
        replyUrl = reply.url()
        
        if replyUrl.scheme() == "abp":
            return
        
        if reply.error() == QNetworkReply.NoError:
            if reply.header(QNetworkRequest.ContentTypeHeader):
                self.mw.downloadManager().handleUnsupportedContent(
                    reply, webPage=self.page(), mainWindow=self.mw)
                return
        
        replyUrl = reply.url()
        if replyUrl.isEmpty():
            return
        
        notFoundFrame = self.page().mainFrame()
        if notFoundFrame is None:
            return
        
        if reply.header(QNetworkRequest.ContentTypeHeader):
            data = reply.readAll()
            if contentSniff(data):
                notFoundFrame.setHtml(str(data, encoding="utf-8"), replyUrl)
                return
        
        urlString = bytes(replyUrl.toEncoded()).decode()
        title = self.tr("Error loading page: {0}").format(urlString)
        htmlFile = QFile(":/html/notFoundPage.html")
        htmlFile.open(QFile.ReadOnly)
        html = htmlFile.readAll()
        pixmap = qApp.style()\
            .standardIcon(QStyle.SP_MessageBoxWarning).pixmap(48, 48)
        imageBuffer = QBuffer()
        imageBuffer.open(QIODevice.ReadWrite)
        if pixmap.save(imageBuffer, "PNG"):
            html = html.replace("@IMAGE@", imageBuffer.buffer().toBase64())
        pixmap = qApp.style()\
            .standardIcon(QStyle.SP_MessageBoxWarning).pixmap(16, 16)
        imageBuffer = QBuffer()
        imageBuffer.open(QIODevice.ReadWrite)
        if pixmap.save(imageBuffer, "PNG"):
            html = html.replace("@FAVICON@", imageBuffer.buffer().toBase64())
        html = html.replace("@TITLE@", title.encode("utf8"))
        html = html.replace("@H1@", reply.errorString().encode("utf8"))
        html = html.replace(
            "@H2@", self.tr("When connecting to: {0}.")
            .format(urlString).encode("utf8"))
        html = html.replace(
            "@LI-1@",
            self.tr("Check the address for errors such as "
                    "<b>ww</b>.example.org instead of "
                    "<b>www</b>.example.org").encode("utf8"))
        html = html.replace(
            "@LI-2@",
            self.tr("If the address is correct, try checking the network "
                    "connection.").encode("utf8"))
        html = html.replace(
            "@LI-3@",
            self.tr(
                "If your computer or network is protected by a firewall "
                "or proxy, make sure that the browser is permitted to "
                "access the network.").encode("utf8"))
        html = html.replace(
            "@LI-4@",
            self.tr("If your cache policy is set to offline browsing,"
                    "only pages in the local cache are available.")
            .encode("utf8"))
        html = html.replace(
            "@BUTTON@", self.tr("Try Again").encode("utf8"))
        notFoundFrame.setHtml(bytes(html).decode("utf8"), replyUrl)
        self.mw.historyManager().removeHistoryEntry(replyUrl, self.title())
        self.loadFinished.emit(False)
    
    def __featurePermissionRequested(self, frame, feature):
        """
        Private slot handling a feature permission request.
        
        @param frame frame sending the request
        @type QWebFrame
        @param feature requested feature
        @type QWebPage.Feature
        """
        manager = Helpviewer.HelpWindow.HelpWindow.featurePermissionManager()
        manager.requestFeaturePermission(self.page(), frame, feature)
    
    def __downloadRequested(self, request):
        """
        Private slot to handle a download request.
        
        @param request reference to the request object (QNetworkRequest)
        """
        self.mw.downloadManager().download(request, mainWindow=self.mw)
    
    def __databaseQuotaExceeded(self, frame, databaseName):
        """
        Private slot to handle the case, where the database quota is exceeded.
        
        @param frame reference to the frame (QWebFrame)
        @param databaseName name of the web database (string)
        """
        securityOrigin = frame.securityOrigin()
        if securityOrigin.databaseQuota() > 0 and \
           securityOrigin.databaseUsage() == 0:
            # cope with a strange behavior of Qt 4.6, if a database is
            # accessed for the first time
            return
        
        res = E5MessageBox.yesNo(
            self,
            self.tr("Web Database Quota"),
            self.tr(
                """<p>The database quota of <strong>{0}</strong> has"""
                """ been exceeded while accessing database <strong>{1}"""
                """</strong>.</p><p>Shall it be changed?</p>""")
            .format(self.__dataString(securityOrigin.databaseQuota()),
                    databaseName),
            yesDefault=True)
        if res:
            newQuota, ok = QInputDialog.getInt(
                self,
                self.tr("New Web Database Quota"),
                self.tr(
                    "Enter the new quota in MB (current = {0}, used = {1}; "
                    "step size = 5 MB):"
                    .format(
                        self.__dataString(securityOrigin.databaseQuota()),
                        self.__dataString(securityOrigin.databaseUsage()))),
                securityOrigin.databaseQuota() // (1024 * 1024),
                0, 2147483647, 5)
            if ok:
                securityOrigin.setDatabaseQuota(newQuota * 1024 * 1024)
    
    def __dataString(self, size):
        """
        Private method to generate a formatted data string.
        
        @param size size to be formatted (integer)
        @return formatted data string (string)
        """
        unit = ""
        if size < 1024:
            unit = self.tr("bytes")
        elif size < 1024 * 1024:
            size /= 1024
            unit = self.tr("kB")
        else:
            size /= 1024 * 1024
            unit = self.tr("MB")
        return "{0:.1f} {1}".format(size, unit)
    
    ###########################################################################
    ## Access key related methods below
    ###########################################################################
    
    def __accessKeyShortcut(self):
        """
        Private slot to switch the display of access keys.
        """
        if not self.hasFocus() or \
           not self.__accessKeysPressed or \
           not self.__enableAccessKeys:
            return
        
        if self.__accessKeyLabels:
            self.__hideAccessKeys()
        else:
            self.__showAccessKeys()
        
        self.__accessKeysPressed = False
    
    def __checkForAccessKey(self, evt):
        """
        Private method to check the existence of an access key and activate the
        corresponding link.
        
        @param evt reference to the key event (QKeyEvent)
        @return flag indicating, if the event was handled (boolean)
        """
        if not self.__accessKeyLabels:
            return False
        
        text = evt.text()
        if not text:
            return False
        
        key = text[0].upper()
        handled = False
        if key in self.__accessKeyNodes:
            element = self.__accessKeyNodes[key]
            p = element.geometry().center()
            frame = element.webFrame()
            p -= frame.scrollPosition()
            frame = frame.parentFrame()
            while frame and frame != self.page().mainFrame():
                p -= frame.scrollPosition()
                frame = frame.parentFrame()
            pevent = QMouseEvent(
                QEvent.MouseButtonPress, p, Qt.LeftButton,
                Qt.MouseButtons(Qt.NoButton),
                Qt.KeyboardModifiers(Qt.NoModifier))
            qApp.sendEvent(self, pevent)
            revent = QMouseEvent(
                QEvent.MouseButtonRelease, p, Qt.LeftButton,
                Qt.MouseButtons(Qt.NoButton),
                Qt.KeyboardModifiers(Qt.NoModifier))
            qApp.sendEvent(self, revent)
            handled = True
        
        return handled
    
    def __hideAccessKeys(self):
        """
        Private slot to hide the access key labels.
        """
        if self.__accessKeyLabels:
            for label in self.__accessKeyLabels:
                label.hide()
                label.deleteLater()
            self.__accessKeyLabels = []
            self.__accessKeyNodes = {}
            self.update()
    
    def __showAccessKeys(self):
        """
        Private method to show the access key labels.
        """
        supportedElements = [
            "input", "a", "area", "button", "label", "legend", "textarea",
        ]
        unusedKeys = "A B C D E F G H I J K L M N O P Q R S T U V W X Y Z" \
            " 0 1 2 3 4 5 6 7 8 9".split()
        
        viewport = QRect(self.__page.mainFrame().scrollPosition(),
                         self.__page.viewportSize())
        # Priority first goes to elements with accesskey attributes
        alreadyLabeled = []
        for elementType in supportedElements:
            result = self.page().mainFrame().findAllElements(elementType)\
                .toList()
            for element in result:
                geometry = element.geometry()
                if geometry.size().isEmpty() or \
                   not viewport.contains(geometry.topLeft()):
                    continue
                
                accessKeyAttribute = element.attribute("accesskey").upper()
                if not accessKeyAttribute:
                    continue
                
                accessKey = ""
                i = 0
                while i < len(accessKeyAttribute):
                    if accessKeyAttribute[i] in unusedKeys:
                        accessKey = accessKeyAttribute[i]
                        break
                    i += 2
                if accessKey == "":
                    continue
                unusedKeys.remove(accessKey)
                self.__makeAccessLabel(accessKey, element)
                alreadyLabeled.append(element)
        
        # Pick an access key first from the letters in the text and then
        # from the list of unused access keys
        for elementType in supportedElements:
            result = self.page().mainFrame().findAllElements(elementType)\
                .toList()
            for element in result:
                geometry = element.geometry()
                if not unusedKeys or \
                   element in alreadyLabeled or \
                   geometry.size().isEmpty() or \
                   not viewport.contains(geometry.topLeft()):
                    continue
                
                accessKey = ""
                text = element.toPlainText().upper()
                for c in text:
                    if c in unusedKeys:
                        accessKey = c
                        break
                if accessKey == "":
                    accessKey = unusedKeys[0]
                unusedKeys.remove(accessKey)
                self.__makeAccessLabel(accessKey, element)
    
    def __makeAccessLabel(self, accessKey, element):
        """
        Private method to generate the access label for an element.
        
        @param accessKey access key to generate the label for (str)
        @param element reference to the web element to create the label for
            (QWebElement)
        """
        label = QLabel(self)
        label.setText("<qt><b>{0}</b></qt>".format(accessKey))
        
        p = QToolTip.palette()
        color = QColor(Qt.yellow).lighter(150)
        color.setAlpha(175)
        p.setColor(QPalette.Window, color)
        label.setPalette(p)
        label.setAutoFillBackground(True)
        label.setFrameStyle(QFrame.Box | QFrame.Plain)
        point = element.geometry().center()
        point -= self.__page.mainFrame().scrollPosition()
        label.move(point)
        label.show()
        point.setX(point.x() - label.width() // 2)
        label.move(point)
        self.__accessKeyLabels.append(label)
        self.__accessKeyNodes[accessKey] = element
    
    ###########################################################################
    ## Miscellaneous methods below
    ###########################################################################
    
    def createWindow(self, windowType):
        """
        Public method called, when a new window should be created.
        
        @param windowType type of the requested window (QWebPage.WebWindowType)
        @return reference to the created browser window (HelpBrowser)
        """
        self.mw.newTab(addNextTo=self)
        return self.mw.currentBrowser()
    
    def preferencesChanged(self):
        """
        Public method to indicate a change of the settings.
        """
        self.__enableAccessKeys = Preferences.getHelp("AccessKeysEnabled")
        if not self.__enableAccessKeys:
            self.__hideAccessKeys()
        
        self.reload()
    
    ###########################################################################
    ## RSS related methods below
    ###########################################################################
    
    def checkRSS(self):
        """
        Public method to check, if the loaded page contains feed links.
        
        @return flag indicating the existence of feed links (boolean)
        """
        self.__rss = []
        
        frame = self.page().mainFrame()
        linkElementsList = frame.findAllElements("link").toList()
        
        for linkElement in linkElementsList:
            # only atom+xml and rss+xml will be processed
            if linkElement.attribute("rel") != "alternate" or \
               (linkElement.attribute("type") != "application/rss+xml" and
                    linkElement.attribute("type") != "application/atom+xml"):
                continue
            
            title = linkElement.attribute("title")
            href = linkElement.attribute("href")
            if href == "" or title == "":
                continue
            self.__rss.append((title, href))
        
        return len(self.__rss) > 0
    
    def getRSS(self):
        """
        Public method to get the extracted RSS feeds.
        
        @return list of RSS feeds (list of tuples of two strings)
        """
        return self.__rss
    
    def hasRSS(self):
        """
        Public method to check, if the loaded page has RSS links.
        
        @return flag indicating the presence of RSS links (boolean)
        """
        return len(self.__rss) > 0
    
    ###########################################################################
    ## Clicked Frame slots
    ###########################################################################
    
    def __loadClickedFrame(self):
        """
        Private slot to load the selected frame only.
        """
        self.setSource(self.__clickedFrame.url())
    
    def __printClickedFrame(self):
        """
        Private slot to print the selected frame.
        """
        printer = QPrinter(mode=QPrinter.HighResolution)
        if Preferences.getPrinter("ColorMode"):
            printer.setColorMode(QPrinter.Color)
        else:
            printer.setColorMode(QPrinter.GrayScale)
        if Preferences.getPrinter("FirstPageFirst"):
            printer.setPageOrder(QPrinter.FirstPageFirst)
        else:
            printer.setPageOrder(QPrinter.LastPageFirst)
        printer.setPageMargins(
            Preferences.getPrinter("LeftMargin") * 10,
            Preferences.getPrinter("TopMargin") * 10,
            Preferences.getPrinter("RightMargin") * 10,
            Preferences.getPrinter("BottomMargin") * 10,
            QPrinter.Millimeter
        )
        printerName = Preferences.getPrinter("PrinterName")
        if printerName:
            printer.setPrinterName(printerName)
        
        printDialog = QPrintDialog(printer, self)
        if printDialog.exec_() == QDialog.Accepted:
            try:
                self.__clickedFrame.print_(printer)
            except AttributeError:
                E5MessageBox.critical(
                    self,
                    self.tr("eric6 Web Browser"),
                    self.tr(
                        """<p>Printing is not available due to a bug in"""
                        """ PyQt5. Please upgrade.</p>"""))
    
    def __printPreviewClickedFrame(self):
        """
        Private slot to show a print preview of the clicked frame.
        """
        from PyQt5.QtPrintSupport import QPrintPreviewDialog
        
        printer = QPrinter(mode=QPrinter.HighResolution)
        if Preferences.getPrinter("ColorMode"):
            printer.setColorMode(QPrinter.Color)
        else:
            printer.setColorMode(QPrinter.GrayScale)
        if Preferences.getPrinter("FirstPageFirst"):
            printer.setPageOrder(QPrinter.FirstPageFirst)
        else:
            printer.setPageOrder(QPrinter.LastPageFirst)
        printer.setPageMargins(
            Preferences.getPrinter("LeftMargin") * 10,
            Preferences.getPrinter("TopMargin") * 10,
            Preferences.getPrinter("RightMargin") * 10,
            Preferences.getPrinter("BottomMargin") * 10,
            QPrinter.Millimeter
        )
        printerName = Preferences.getPrinter("PrinterName")
        if printerName:
            printer.setPrinterName(printerName)
        
        preview = QPrintPreviewDialog(printer, self)
        preview.paintRequested.connect(self.__generatePrintPreviewClickedFrame)
        preview.exec_()
    
    def __generatePrintPreviewClickedFrame(self, printer):
        """
        Private slot to generate a print preview of the clicked frame.
        
        @param printer reference to the printer object (QPrinter)
        """
        try:
            self.__clickedFrame.print_(printer)
        except AttributeError:
            E5MessageBox.critical(
                self,
                self.tr("eric6 Web Browser"),
                self.tr(
                    """<p>Printing is not available due to a bug in PyQt5."""
                    """Please upgrade.</p>"""))
            return
    
    def __printPdfClickedFrame(self):
        """
        Private slot to print the selected frame to PDF.
        """
        printer = QPrinter(mode=QPrinter.HighResolution)
        if Preferences.getPrinter("ColorMode"):
            printer.setColorMode(QPrinter.Color)
        else:
            printer.setColorMode(QPrinter.GrayScale)
        printerName = Preferences.getPrinter("PrinterName")
        if printerName:
            printer.setPrinterName(printerName)
        printer.setOutputFormat(QPrinter.PdfFormat)
        name = self.__clickedFrame.url().path().rsplit('/', 1)[-1]
        if name:
            name = name.rsplit('.', 1)[0]
            name += '.pdf'
            printer.setOutputFileName(name)
        
        printDialog = QPrintDialog(printer, self)
        if printDialog.exec_() == QDialog.Accepted:
            try:
                self.__clickedFrame.print_(printer)
            except AttributeError:
                E5MessageBox.critical(
                    self,
                    self.tr("eric6 Web Browser"),
                    self.tr(
                        """<p>Printing is not available due to a bug in"""
                        """ PyQt5. Please upgrade.</p>"""))
                return
    
    def __zoomInClickedFrame(self):
        """
        Private slot to zoom into the clicked frame.
        """
        index = self.__levelForZoom(
            int(self.__clickedFrame.zoomFactor() * 100))
        if index < len(self.__zoomLevels) - 1:
            self.__clickedFrame.setZoomFactor(
                self.__zoomLevels[index + 1] / 100)
    
    def __zoomResetClickedFrame(self):
        """
        Private slot to reset the zoom factor of the clicked frame.
        """
        self.__clickedFrame.setZoomFactor(self.__currentZoom / 100)
    
    def __zoomOutClickedFrame(self):
        """
        Private slot to zoom out of the clicked frame.
        """
        index = self.__levelForZoom(
            int(self.__clickedFrame.zoomFactor() * 100))
        if index > 0:
            self.__clickedFrame.setZoomFactor(
                self.__zoomLevels[index - 1] / 100)
    
    def __showClickedFrameSource(self):
        """
        Private slot to show the source of the clicked frame.
        """
        from QScintilla.MiniEditor import MiniEditor
        src = self.__clickedFrame.toHtml()
        editor = MiniEditor(parent=self)
        editor.setText(src, "Html")
        editor.setLanguage("dummy.html")
        editor.show()
    
    ###########################################################################
    ## Speed Dial slots below
    ###########################################################################
    
    def __addSpeedDial(self):
        """
        Private slot to add a new speed dial.
        """
        self.page().mainFrame().evaluateJavaScript("addSpeedDial();")
    
    def __configureSpeedDial(self):
        """
        Private slot to configure the speed dial.
        """
        self.page().mainFrame().evaluateJavaScript("configureSpeedDial();")
    
    def __reloadAllSpeedDials(self):
        """
        Private slot to reload all speed dials.
        """
        self.page().mainFrame().evaluateJavaScript("reloadAll();")
    
    def __resetSpeedDials(self):
        """
        Private slot to reset all speed dials to the default pages.
        """
        self.__speedDial.resetDials()


def contentSniff(data):
    """
    Module function to do some content sniffing to check, if the data is HTML.
    
    @param data data block to sniff at (string)
    @return flag indicating HTML content (boolean)
    """
    if data.contains("<!doctype") or \
       data.contains("<script") or \
       data.contains("<html") or \
       data.contains("<!--") or \
       data.contains("<head") or \
       data.contains("<iframe") or \
       data.contains("<h1") or \
       data.contains("<div") or \
       data.contains("<font") or \
       data.contains("<table") or \
       data.contains("<a") or \
       data.contains("<style") or \
       data.contains("<title") or \
       data.contains("<b") or \
       data.contains("<body") or \
       data.contains("<br") or \
       data.contains("<p"):
        return True
    
    return False