Update kses and TinyMCE to allow select data-* attributes in WordPress

data-attributes.php

<?php

add_action( 'after_setup_theme', 'x_kses_allow_data_attributes_on_links' );
function x_kses_allow_data_attributes_on_links() {
  global $allowedposttags;

	$tags = array( 'a' );
	$new_attributes = array(
		'data-foo' => array(),
		'data-bar' => array(),
	);

	foreach ( $tags as $tag ) {
		if ( isset( $allowedposttags[ $tag ] ) && is_array( $allowedposttags[ $tag ] ) )
			$allowedposttags[ $tag ] = array_merge( $allowedposttags[ $tag ], $new_attributes );
	}
}

add_filter( 'tiny_mce_before_init', 'x_tinymce_allow_data_attributes_on_links' );
function x_tinymce_allow_data_attributes_on_links( $options ) { 
	if ( ! isset( $options['extended_valid_elements'] ) ) 
		$options['extended_valid_elements'] = ''; 

	$options['extended_valid_elements'] .= ',a[data-foo|data-bar|class|id|style|href]';

	return $options; 
}