do_shortcode_tag( array $m )

function do_shortcode_tag( $m ) {
	global $shortcode_tags;

	// allow [[foo]] syntax for escaping a tag
	if ( $m[1] == '[' && $m[6] == ']' ) {
		return substr($m[0], 1, -1);
	}

	$tag = $m[2];
	$attr = shortcode_parse_atts( $m[3] );

	if ( ! is_callable( $shortcode_tags[ $tag ] ) ) {
		/* translators: %s: shortcode tag */
		$message = sprintf( __( 'Attempting to parse a shortcode without a valid callback: %s' ), $tag );
		_doing_it_wrong( __FUNCTION__, $message, 'WP-4.3.0' );
		return $m[0];
	}

	/**
	 * Filters whether to call a shortcode callback.
	 *
	 * Passing a truthy value to the filter will effectively short-circuit the
	 * shortcode generation process, returning that value instead.
	 *
	 * @since WP-4.7.0
	 *
	 * @param bool|string $return      Short-circuit return value. Either false or the value to replace the shortcode with.
	 * @param string       $tag         Shortcode name.
	 * @param array|string $attr        Shortcode attributes array or empty string.
	 * @param array        $m           Regular expression match array.
	 */
	$return = apply_filters( 'pre_do_shortcode_tag', false, $tag, $attr, $m );
	if ( false !== $return ) {
		return $return;
	}

	$content = isset( $m[5] ) ? $m[5] : null;

	$output = $m[1] . call_user_func( $shortcode_tags[ $tag ], $attr, $content, $tag ) . $m[6];

	/**
	 * Filters the output created by a shortcode callback.
	 *
	 * @since WP-4.7.0
	 *
	 * @param string       $output Shortcode output.
	 * @param string       $tag    Shortcode name.
	 * @param array|string $attr   Shortcode attributes array or empty string.
	 * @param array        $m      Regular expression match array.
	 */
	return apply_filters( 'do_shortcode_tag', $output, $tag, $attr, $m );
}