RM

add_action( 'rank_math/vars/register_extra_replacements', function(){
    rank_math_register_var_replacement(
       'limit_description',
       [
       'name'        => esc_html__( 'name', 'rank-math' ),
       'description' => esc_html__( 'description', 'rank-math' ),
       'variable'    => 'limit_description',
       'example'     => limit_description_callback(),
       ],
       'limit_description_callback'
   );
});
function limit_description_callback(){
    $content = get_the_content();
    return substr(strip_tags($content), 0, 250);
}