[Mediawiki-l] Extension help: why is text appearing twice?

[Daniel Barrett]

>You might try OutputPageBeforeHTML.
>Rob Church

Unfortunately OutputPageBeforeHTML doesn't work -- my output doesn't
appear at all on the page.

Here's the extension again:

$wgHooks['OutputPageBeforeHTML'][] = 'Problem';
function Problem(&$parser, &$text) {
  $text = "$text abc";
}

Any other suggestions?
DanB