MediaWiki Extension question / suggestion - mediawiki

Question

Complete beginner here. I want to create a new tab on each page that has a custom action. When clicked, it takes you to a new page which has custom HTML on it along with the text or the original article.
So far I could create a new Tab and could give a custom action mycustomaction to it. I am pasting what I did so far here. Please let me know if I am using the correct hooks etc. and what is a better way to achieve this basic functionality.
So far with their docs I have done this:
#Hook for Tab
$wgHooks['SkinTemplateContentActions'][] = 'myTab';
#Callback
function myTab( $content_actions) {
global $wgTitle;
$content_actions['0'] = array(
'text' => 'my custom label',
'href' => $wgTitle->getFullURL( 'action=mycustomaction' ),
);
return true;
}
#new action hook
$wgHooks['UnknownAction'][] = 'mycustomaction';
#callback
function mycustomaction($action, $article) {
echo $action;
return true;
}
This gives me error:
No such action
The action specified by the URL is invalid. You might have mistyped the URL, or followed an incorrect link. This might also indicate a bug in the software used by yourplugin

Answer 1

What I was doing wrong:
$content_actions[‘0’] should simply be $content_actions[] (minor nitpick)
$content_actions is passed-by-reference, it should be function myTab( &$content_actions ) {}
mycustomaction() should do something along the lines of
if ( $action == ‘mycustomaction’ ) {
do stuff; return false;
}
else {
return true;
}
It should use $wgOut->addHTML() instead of echo
Thanks a lot everyone for your help!