What is the exact difference between esc_html and wp_filter_nohtml_kses. Everywhere I look says that both strip all the html, the only difference I can see is to do with exactly how they do this. Does esc_html encode the tags and does wp_filter_nohtml_kses strip them altogether?
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Contrary to what you have been looking at, esc_html does not strip all the HTML, it escapes it, meaning it encodes it into safe HTML entities that do not break HTML tags.
wp_filter_nohtml_kses strips all the HTML.
When in doubt always consult the source code. It is accessible online.
esc_attr is short and sweet, uses _wp_specialchars, defined in wp-includes/formatting.php
wp_filter_nohtml_kses is defined in wp-includes/kses.php, and “Strips all of the HTML in the content.“