Missing doc for QT_DEBUG_PLUGINS

The page How to Create Qt Plugins used to mention the QT_DEBUG_PLUGINS environment variable (as of Qt 4.2, at least, as seen at <http://qt.nokia.com/doc/4.2/plugins-howto.html>).

But the current version of this page no longer mentions QT_DEBUG_PLUGINS. Nor does any other page in the current Qt documentation. Look up QT_DEBUG_PLUGINS in Qt Creator's help system index, and it will take you to the How to Create Qt Plugins page, but the page itself doesn't mention that environment variable, despite being indexed as if it did.

The documentation for this useful environment variable should be restored.