Clarify documentation for QKeyEvent::text

Change-Id: I4b455a512b2e678b6127ea488b456c68eb80cdbc
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>

src/gui/kernel/qevent.cpp

@@ -947,11 +947,14 @@ QKeyEvent::~QKeyEvent()
 /*!
     \fn QString QKeyEvent::text() const
 
-    Returns the Unicode text that this key generated. The text
-    returned can be an empty string in cases
-    where modifier keys, such as Shift, Control, Alt, and Meta,
-    are being pressed or released. In such cases key() will contain
-    a valid value.
+    Returns the Unicode text that this key generated.
+
+    Return values when modifier keys such as
+    Shift, Control, Alt, and Meta are pressed
+    differ among platforms and could return an empty string.
+
+    \note \l key() will always return a valid value,
+    independent of modifier keys.
 
     \sa Qt::WA_KeyCompression
 */