Sometimes content is outputted somewhere where I don’t need (when I run do_action), and I can’t really see what action does that. So to get the list of WordPress actions attached to a hook, use this kind of code:
global $wp_filter; var_dump($wp_filter['comment_form']);
You will get then something like this:
array(1) { [10]=> array(2) { ["wp_comment_form_unfiltered_html_nonce"]=> array(2) { ["function"]=> string(37) "wp_comment_form_unfiltered_html_nonce" ["accepted_args"]=> int(1) } ["akismet_add_comment_nonce"]=> array(2) { ["function"]=> string(25) "akismet_add_comment_nonce" ["accepted_args"]=> int(1) } } }
Pretty cool, now we know what produces all that output.
