wfRunHooks( 'ParserMakeImageParams', array( $title, $file, &$params ) );What is there to know? It's one line of code.
You need to know what $title, $file and $params are, and where exactly in the process the line of code appears. Sure, anyone can read the code and work that out fairly easily, but the person that just added the hook already knows and can do it without looking it up.