[wp-hackers] Adding Filters

[Andrew Nacin]

>
> add_filter ('get_post_custom_values', 'anti_email_spam', 16);
>

You should read through the Plugin API in the Codex:
http://codex.wordpress.org/Plugin_API.

You don't add a filter to a function; you add it to an API hook that is
built into the WordPress core. the_content() happens to be a function, but
it is also the name of a hook that filters the content returned by that
function, and that's what you're applying the filter to. (
http://adambrown.info/p/wp_hooks/hook/the_content?version=2.8&file=wp-includes/post-template.php--
it also is a filter in a few other spots.)