I'm trying to add a PureCSS class to the <form> tag in the default comments template, but the class isn't being added. Here's what I've done so far:

function pwp_comments_form_pure($output) {
    $output = preg_replace('/class="comment-form"/', 'class="comment-form pure-form"', $output);
    return $output;
add_filter('comments_template', 'pwp_comments_form_pure');

I know the preg_replace approach works, because I did the same for the default search form and it worked without any problems:

function pwp_search_form_pure($output) {
    $output = preg_replace('/class="searchform"/', 'class="searchform pure-form"', $output);
    return $output;
add_filter('get_search_form', 'pwp_search_form_pure');

I've triple-checked the class names and hyphenation, and they all match up.

I've also tried adding a priority parameter of 1 and 100 to the comments_template filter, but it didn't make a difference.

Is there an override somewhere in the WordPress defaults that I'm not aware of?


Any comments_template filter should return an absolute filepath to the comments template - use comment_form_defaults and set the class_form argument:

add_filter( 'comment_form_defaults', function ( $args ) {
    $args['class_form'] = 'my form classes';
    return $args;
  • That's exactly what I needed, thank you. I hadn't fully appreciated that comments_template was actually for templates! – tristanojbacon Oct 4 '16 at 15:22

The filter you are using is about the template path, it doesn't do anything with the form output. The class you want to add doesn't need a filter. You can set it when you set the arguments for your call to comment_form in your template.

$comment_args        =  array (
  'id_form'         =>  'comment-form',
  'class_form'      =>  'comment-form pure-form',
$comment_form ($comment_args);
  • 1
    An equally good solution, and the only reason I didn't accept it was because I need a solution that sits in my theme's functions.php file, rather than in the template. – tristanojbacon Oct 4 '16 at 15:23

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