P̶l̶a̶c̶e̶h̶o̶l̶d̶e̶r̶ Default content in Custom Post Type TinyMCE editor

Question

There is no way to add “placeholder” for TinyMCE, but you can set default content for newly created posts. All you need is just to hook default_content filter and return your formatted paragraphs:

add_filter( 'default_content', 'wpse8170_get_default_instructions', 10, 2 );
function wpse8170_get_default_instructions( $content, WP_Post $post ) {
    if ( $post->post_type == 'post' ) {
        $content=".... your content ....";
    }
    return $content;
}