Ticket #52133: test-code.php

<?php
add_action( 'add_meta_boxes', 'mcdev_add_meta_to_posts' );

function mcdev_add_meta_to_posts() {
        // Add new meta box.
        add_meta_box(
                'mcdev_post_note_box',
                'Test TinyMCE Note',
                'mcev_render_meta_posts_content',
                'post',
                'normal'
        );
}

function mcev_render_meta_posts_content() {
        global $post;

        // Get saved meta data.
        $post_note_meta_content = get_post_meta( $post->ID, 'mcdev_post_note', true );

        // Hidden nonce field.
        wp_nonce_field( 'mcdev_post_note' . $post->ID, 'mcdev_post_note_nonce' );

        // Render editor metabox.
        wp_editor( $post_note_meta_content, 'mcdev_post_note', array( 'textarea_rows' => '5' ) );
}

add_action( 'save_post', 'post_note_meta_box_save' );

function post_note_meta_box_save( $post_id ) {
        // Bail if auto save.
        if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
                return;
        }

        // Bail if nonce is missing or nonce verification fails.
        if ( ! isset( $_POST['mcdev_post_note_nonce'] ) || ! wp_verify_nonce( $_POST['mcdev_post_note_nonce'], 'mcdev_post_note' . $post_id ) ) {
                return;
        }

        // Bail is current user is allowed to edit posts.
        if ( ! current_user_can( 'edit_post' ) ) {
                return;
        }

        // Make sure our data is set before trying to save it.
        if ( isset( $_POST['mcdev_post_note'] ) ) {
                update_post_meta( $post_id, 'mcdev_post_note', $_POST['mcdev_post_note'] );
        }
}