Fix for Mark Jaquith's "Markdown on Save" WordPress plugin on WordPress 4.4

markdown-on-save-4-4-fix.php

<?php
/**
 * Plugin Name: Markdown on Save 4.4. Fix
 * Plugin URI: https://gist.github.com/salcode/b6b298a77f1c35cfce1c
 * Description: Temporary fix for https://github.com/markjaquith/markdown-on-save/issues/13, which appears in WordPress 4.4 when running Markdown on Save 1.2.1
 * Version: 1.0.0
 * Author: Sal Ferrarello
 * Author URI: http://salferrarello.com/
 * Text Domain: markdown-on-save-4-4-fix
 *
 * Download from Command Line:
 * curl -O https://gist.githubusercontent.com/salcode/b6b298a77f1c35cfce1c/raw/markdown-on-save-4-4-fix.php
 *
 * @package salcode/markdown-on-save-4-4-fix
 */

// If this file is called directly, abort.
if ( ! defined( 'WPINC' ) ) {
	die;
}

add_action( 'post_submitbox_misc_actions', 'fe_mos_4_4_fix' );

/**
 * Add CSS to force hidden checkbox to display
 *
 * Add this CSS only when 'Markdown on Save' 1.2.1 is active
 */
function fe_mos_4_4_fix() {

	if ( ! is_plugin_active( 'markdown-on-save/markdown-on-save.php' ) ) {
		return;
	}

	$plugin_data = get_plugin_data( WP_PLUGIN_DIR . '/markdown-on-save/markdown-on-save.php' );
	if ( ! isset( $plugin_data['Version'] ) || '1.2.1' !== $plugin_data['Version'] ) {
		return;
	}
	?>
		<style>
			#cws_using_markdown { display: block !important; margin: 0 0 10px 10px; }
			#cws_using_markdown::after { content: "Markdown"; display: block; padding: 8px 0 0 20px; }
		</style>
	<?php
}