/**

 * Add the unfiltered_html capability to the editor role.

 * Be careful which users you grant this capability to.

 */

add_filter( 'map_meta_cap', function ( $caps, $cap, $user_id ) {

	// Change editor with the user role you want to allow to use unfiltered_html.

	if ( 'unfiltered_html' === $cap && user_can( $user_id, 'editor' ) ) {

		$caps = array( 'unfiltered_html' );

	}

	return $caps;

}, 1, 3 );