How to filter post titles

If you know that you will want to apply a filter to all of your post titles in WordPress, such as forcing uppercase, lowercase, or title capitalization, you can use a filter to do so. The filter below will force a title to lowercase as the post is saved:

if ( !function_exists( 'ucc_post_title_filter' ) ) :
  function ucc_post_title_filter( $data ) {
    $title = $data['post_title'];

    $title = strtolower( $title );
    $data['post_title'] = $title;

    return( $data );
  add_filter( 'wp_insert_post_data' , 'ucc_post_title_filter' );

On line 5, strtolower() can be exchanged for any text-transforming function.