The onBeforePagesSaveFilter handler runs during the page save process in LiveWhale CMS after the page buffer has been validated to prevent all errors but before it completes the save process.

<?php
    $_LW->REGISTERED_APPS['my_app']=[
       'title'=>'My App',
       'handlers'=>['onBeforePagesSaveFilter'],
    ];

    class LiveWhaleApplicationMyApp {

      public function onBeforePagesSaveFilter($buffer) { 
        global $_LW;

        // Do whatever you want to $buffer here...

        return $buffer;
      }

   }
?>

Note, the resulting $buffer will still get passed through LiveWhale’s internal page formatting tool, so certain markup changes you make might get reformatted or respelled after your handler is run.