Fix QRegularExpressionMatch capture-related documentation

The documentation is not explicit enough about the content of the
returned list of capturedList nor the element 0 when calling captured or
its friends.

The first element (aka element 0) is the whole string captured when one
or more groups are used.

Change-Id: I3c59ebfc9f6d762dd4d8aaf8f5c0de24359f53d7
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Sze Howe Koh <szehowe.koh@gmail.com>

src/corelib/tools/qregularexpression.cpp

@@ -2138,6 +2138,9 @@ int QRegularExpressionMatch::lastCapturedIndex() const
     If the \a nth capturing group did not capture a string, or if there is no
     such capturing group, returns a null QString.
 
+    \note The implicit capturing group number 0 captures the substring matched
+    by the entire pattern.
+
     \sa capturedRef(), capturedView(), lastCapturedIndex(), capturedStart(), capturedEnd(),
     capturedLength(), QString::isNull()
 */
@@ -2160,6 +2163,9 @@ QString QRegularExpressionMatch::captured(int nth) const
     If the \a nth capturing group did not capture a string, or if there is no
     such capturing group, returns a null QStringRef.
 
+    \note The implicit capturing group number 0 captures the substring matched
+    by the entire pattern.
+
     \sa captured(), capturedView(), lastCapturedIndex(), capturedStart(), capturedEnd(),
     capturedLength(), QStringRef::isNull()
 */
@@ -2184,6 +2190,9 @@ QStringRef QRegularExpressionMatch::capturedRef(int nth) const
     If the \a nth capturing group did not capture a string, or if there is no
     such capturing group, returns a null QStringView.
 
+    \note The implicit capturing group number 0 captures the substring matched
+    by the entire pattern.
+
     \sa captured(), capturedRef(), lastCapturedIndex(), capturedStart(), capturedEnd(),
     capturedLength(), QStringView::isNull()
 */
@@ -2296,7 +2305,9 @@ QStringView QRegularExpressionMatch::capturedView(QStringView name) const
 
 /*!
     Returns a list of all strings captured by capturing groups, in the order
-    the groups themselves appear in the pattern string.
+    the groups themselves appear in the pattern string. The list includes the
+    implicit capturing group number 0, capturing the substring matched by the
+    entire pattern.
 */
 QStringList QRegularExpressionMatch::capturedTexts() const
 {