Clarify documentation of QWebEnginePage::title()

Explain what happens when the HTML has no proper <title> defined and clarify the
meaning of 'by default': it refers to the state before load()/setUrl()/etc.

Fixes: QTBUG-71799
Change-Id: Ib2669007573b3ea53e205d9228237bae392f6f78
Reviewed-by: Michael Brüning <michael.bruning@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

src/webenginewidgets/doc/src/qwebenginepage_lgpl.qdoc

@@ -643,6 +643,12 @@
     \property QWebEnginePage::title
     \brief the title of the page as defined by the HTML \c <title> element
 
+    If the page has no \c <title> element, then the URL is used instead. For \c
+    file:// URLs only the filename is used and not the full path.
+
+    By default, before any content has been loaded, this property contains an
+    empty string.
+
     \sa titleChanged()
 */
 

src/webenginewidgets/doc/src/qwebengineview_lgpl.qdoc

@@ -173,9 +173,9 @@
 
 /*!
     \property QWebEngineView::title
-    \brief the title of the web page currently viewed
+    \brief the title of the page as defined by the HTML \c <title> element
 
-    By default, this property contains an empty string.
+    Equivalent to \l {QWebEnginePage::title()}.
 
     \sa titleChanged()
 */