Return instead of echoing.

md_rioe.php

<?php
/**
 * This function can be used to return (instead of echoing) results
 * of build-in functions, that cannot return, just echo.
 * @return mixed  Results of called function.
 */
function md_rioe() {
    
    if (func_num_args() === 0) {
        trigger_error('Nothing to call', E_USER_WARNING);
        return;
    }
    
    ob_start();
    
    if (func_num_args() === 1) {
        call_user_func(func_get_arg(0));
    } elseif (func_num_args() > 1) {
        $args = array_slice(func_get_args(), 1);
        call_user_func_array(func_get_arg(0), $args);
    }
    
    return ob_get_clean();
    
}

// Examples.
// wp_head();
$wp_head = md_rioe('wp_head');

// body_class('additional-class');
$body_class = md_rioe('body_class', 'additional-class');

// wp_editor('content', 'editor_id', [
//     'wpautop' => false
// ]);
$wp_editor = md_rioe('wp_editor', 'content', 'editor_id', [
    'wpautop' => false
]);