* WordPress API for creating bbcode-like tags or what WordPress calls

 * "shortcodes". The tag and attribute parsing or regular expression code is

 * Adds a new shortcode.

 * Care should be taken through prefixing or other means to ensure that the

 * shortcode tag being added is unique and will not conflict with other,

 * already-added shortcode tags. In the event of a duplicated tag, the tag

 * loaded last will take precedence.

 * @global array $shortcode_tags

 * @param string   $tag      Shortcode tag to be searched in post content.

 * @param callable $callback The callback function to run when the shortcode is found.

 *                           Every shortcode callback is passed three parameters by default,

 *                           including an array of attributes (`$atts`), the shortcode content

 *                           or null if not set (`$content`), and finally the shortcode tag

 *                           itself (`$shortcode_tag`), in that order.

function add_shortcode( $tag, $callback ) {

	if ( '' == trim( $tag ) ) {

		$message = __( 'Invalid shortcode name: Empty name given.' );

		_doing_it_wrong( __FUNCTION__, $message, '4.4.0' );

		return;

	}

	if ( 0 !== preg_match( '@[<>&/\[\]\x00-\x20=]@', $tag ) ) {

		/* translators: 1: shortcode name, 2: space separated list of reserved characters */

		$message = sprintf( __( 'Invalid shortcode name: %1$s. Do not use spaces or reserved characters: %2$s' ), $tag, '& / < > [ ] =' );

		_doing_it_wrong( __FUNCTION__, $message, '4.4.0' );

		return;

	}

	$shortcode_tags[ $tag ] = $callback;

 * @global array $shortcode_tags

 * @global array $shortcode_tags

		preg_match_all( '/' . get_shortcode_regex() . '/', $content, $matches, PREG_SET_ORDER );

 * @param bool $ignore_html When true, shortcodes inside HTML elements will be skipped.

function do_shortcode( $content, $ignore_html = false ) {

	// Find all registered tag names in $content.

	preg_match_all( '@\[([^<>&/\[\]\x00-\x20=]++)@', $content, $matches );

	$tagnames = array_intersect( array_keys( $shortcode_tags ), $matches[1] );

	if ( empty( $tagnames ) ) {

		return $content;

	}

	$content = do_shortcodes_in_html_tags( $content, $ignore_html, $tagnames );

	$pattern = get_shortcode_regex( $tagnames );

	$content = preg_replace_callback( "/$pattern/", 'do_shortcode_tag', $content );

	// Always restore square braces so we don't break things like <!--[if IE ]>

	$content = unescape_invalid_shortcodes( $content );

	return $content;

 * @since 4.4.0 Added the `$tagnames` parameter.

 * @global array $shortcode_tags

 * @param array $tagnames Optional. List of shortcodes to find. Defaults to all registered shortcodes.

function get_shortcode_regex( $tagnames = null ) {

	if ( empty( $tagnames ) ) {

		$tagnames = array_keys( $shortcode_tags );

	}

 *

 * @global array $shortcode_tags

 * @return string|false False on failure.

	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, '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 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 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 );

}

/**

 * Search only inside HTML elements for shortcodes and process them.

 *

 * Any [ or ] characters remaining inside elements will be HTML encoded

 * to prevent interference with shortcodes that are outside the elements.

 * Assumes $content processed by KSES already.  Users with unfiltered_html

 * capability may get unexpected output if angle braces are nested in tags.

 *

 * @since 4.2.3

 *

 * @param string $content Content to search for shortcodes

 * @param bool $ignore_html When true, all square braces inside elements will be encoded.

 * @param array $tagnames List of shortcodes to find.

 * @return string Content with shortcodes filtered out.

 */

function do_shortcodes_in_html_tags( $content, $ignore_html, $tagnames ) {

	// Normalize entities in unfiltered HTML before adding placeholders.

	$trans = array( '[' => '[', ']' => ']' );

	$content = strtr( $content, $trans );

	$trans = array( '[' => '[', ']' => ']' );

	$pattern = get_shortcode_regex( $tagnames );

	$textarr = wp_html_split( $content );

	foreach ( $textarr as &$element ) {

		if ( '' == $element || '<' !== $element[0] ) {

			continue;

		}

		$noopen = false === strpos( $element, '[' );

		$noclose = false === strpos( $element, ']' );

		if ( $noopen || $noclose ) {

			// This element does not contain shortcodes.

			if ( $noopen xor $noclose ) {

				// Need to encode stray [ or ] chars.

				$element = strtr( $element, $trans );

			}

			continue;

		}

		if ( $ignore_html || '<!--' === substr( $element, 0, 4 ) || '<![CDATA[' === substr( $element, 0, 9 ) ) {

			// Encode all [ and ] chars.

			$element = strtr( $element, $trans );

			continue;

		}

		$attributes = wp_kses_attr_parse( $element );

		if ( false === $attributes ) {

			// Some plugins are doing things like [name] <[email]>.

			if ( 1 === preg_match( '%^<\s*\[\[?[^\[\]]+\]%', $element ) ) {

				$element = preg_replace_callback( "/$pattern/", 'do_shortcode_tag', $element );

			}

			// Looks like we found some crazy unfiltered HTML.  Skipping it for sanity.

			$element = strtr( $element, $trans );

			continue;

		}

		// Get element name

		$front = array_shift( $attributes );

		$back = array_pop( $attributes );

		$matches = array();

		preg_match('%[a-zA-Z0-9]+%', $front, $matches);

		$elname = $matches[0];

		// Look for shortcodes in each attribute separately.

		foreach ( $attributes as &$attr ) {

			$open = strpos( $attr, '[' );

			$close = strpos( $attr, ']' );

			if ( false === $open || false === $close ) {

				continue; // Go to next attribute.  Square braces will be escaped at end of loop.

			}

			$double = strpos( $attr, '"' );

			$single = strpos( $attr, "'" );

			if ( ( false === $single || $open < $single ) && ( false === $double || $open < $double ) ) {

				// $attr like '[shortcode]' or 'name = [shortcode]' implies unfiltered_html.

				// In this specific situation we assume KSES did not run because the input

				// was written by an administrator, so we should avoid changing the output

				// and we do not need to run KSES here.

				$attr = preg_replace_callback( "/$pattern/", 'do_shortcode_tag', $attr );

			} else {

				// $attr like 'name = "[shortcode]"' or "name = '[shortcode]'"

				// We do not know if $content was unfiltered. Assume KSES ran before shortcodes.

				$count = 0;

				$new_attr = preg_replace_callback( "/$pattern/", 'do_shortcode_tag', $attr, -1, $count );

				if ( $count > 0 ) {

					// Sanitize the shortcode output using KSES.

					$new_attr = wp_kses_one_attr( $new_attr, $elname );

					if ( '' !== trim( $new_attr ) ) {

						// The shortcode is safe to use now.

						$attr = $new_attr;

					}