In my attempt to alter navigations current-menu-item class, I found a possible solution https://stackoverflow.com/a/7941864/520265 ,
add_filter('nav_menu_css_class', 'my_css_attributes_filter', 100, 1);
He makes use of a filter who is called with a tag ‘nav_menu_css_class’ , But it got me wondering, where can you find information about what filters are available to use?
http://codex.wordpress.org/Function_Reference/wp_nav_menu does not mention anything about filters…
There are multiple was to find filters:
Use an IDE (see Eclipse example), set WordPress as a separate project and search in this project for
apply_filtersordo_action.Get a program to search in all files of a directory (grep, Notepad++) and do the same search with that.
Read the source code. If you start with
wp_nav_menu()and follow the functions called in its definition you will find the filters and actions you need.Some of the available filters are listed in the WordPress Codex
Adam Brown hosts a much more complete list of action and filter hooks.
You can also search through the source, as @toscho mentioned.
Also you can use the plugin Debug Objects; the plugin list action and filter hooks on the current page or all hooks.