I think woocommerce_proceed_to_checkout is an action, not a filter. See http://hookr.io/actions/woocommerce_proceed_to_checkout/. For the difference between actions and filters check out this question: Difference Between Filter and Action Hooks?
Above-the-fold inline styles from SASS generated stylesheet
register_activation_hook not updating
How do I trigger a post update within a get_posts() foreach loop?
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As @Jacob mentioned, is an generic utility function used in many contexts and therefore, you might want to either use other approach or hook it selectively through other hook where you would have $post object (e.g. edit_post or other way to define if the post edited is of page type. Something along these lines: <?php … Read more
Footer.php being inserted before article closing tag?
Use like this. add_filter( ‘password_change_email’, ‘wpse207879_change_password_mail_message’, 10, 3 ); function wpse207879_change_password_mail_message( $pass_change_mail, $user, $userdata ) { $new_message_txt = __( ‘Some text ###USERNAME### more text even more text ###EMAIL### more text after more text last bit of text ###SITENAME###’ ); $pass_change_mail[ ‘message’ ] = $new_message_txt; return $pass_change_mail; } Reference of the above code is: Change Password … Read more