WordPress at a glance
filter is not described

mce_css filter-hook . WP 2.1.0

Filters the comma-delimited list of stylesheets to load in TinyMCE.

Usage

add_filter( 'mce_css', 'filter_function_name_2658' );
function filter_function_name_2658( $stylesheets ){
	// filter...

	return $stylesheets;
}
$stylesheets(string)
Comma-delimited list of stylesheets.

Where the hook is called

_WP_Editors::editor_settings()
mce_css
wp-includes/class-wp-editor.php 548
$mce_css = trim( apply_filters( 'mce_css', $mce_css ), ' ,' );

Where the hook is used (in WP core)

Does not used.