Default filter and action functions

[Sceptres]

I am currently working on a plugin and I wanted to see the default implementation of the filter, as in what code runs if there isn't a plugin using this filter. Where can I find this information?

[dgw]

If there's no plugin hooking into the filter, nothing runs.

For more information about the context of a given filter or action, search for its name in the source code. You'll find a yourls_apply_filter or yourls_do_action function call whose surroundings will tell you precisely what happens before and after that filter/action happens.

[ozh]

What @dgw said. Basically a filter is :

$some_value = yourls_apply_filter( 'filter_name', $other_value );

function yourls_apply_filter( $filter_name, $value ) {
    if $filter_name is registered : 
        return the_function_attached_to_the_filter( $value );
    else : 
        return $value;
}

So, nothing hooked to a filter = no code run except the return $value part.