What does apply_filters(…) actually do in WordPress?
original source : http://stackoverflow.com/questions/2270989/what-does-apply-filters-actually-do-in-wordpress
apply_filters($tag, $value) passes the ‘value’ argument to each of the functions ‘hooked’ (using
add_filter) into the specified filter ‘tag’. Each function performs some processing on the value and returns a modified value to be passed to the next function in the sequence.
For example, by default (in WordPress 2.9) the
the_content filter passes the value through the following sequence of functions: