ning bracket for escaping shortcodes: [[tag]]
		. "($tagregexp)"                     // 2: Shortcode name
		. '(?![\\w-])'                       // Not followed by word character or hyphen
		. '('                                // 3: Unroll the loop: Inside the opening shortcode tag
		.     '[^\\]\\/]*'                   // Not a closing bracket or forward slash
		.     '(?:'
		.         '\\/(?!\\])'               // A forward slash not followed by a closing bracket
		.         '[^\\]\\/]*'               // Not a closing bracket or forward slash
		.     ')*?'
		. ')'
		. '(?:'
		.     '(\\/)'                        // 4: Self closing tag ...
		.     '\\]'                          // ... and closing bracket
		. '|'
		.     '\\]'                          // Closing bracket
		.     '(?:'
		.         '('                        // 5: Unroll the loop: Optionally, anything between the opening and closing shortcode tags
		.             '[^\\[]*+'             // Not an opening bracket
		.             '(?:'
		.                 '\\[(?!\\/\\2\\])' // An opening bracket not followed by the closing shortcode tag
		.                 '[^\\[]*+'         // Not an opening bracket
		.             ')*+'
		.         ')'
		.         '\\[\\/\\2\\]'             // Closing shortcode tag
		.     ')?'
		. ')'
		. '(\\]?)';                          // 6: Optional second closing brocket for escaping shortcodes: [[tag]]
}

/**
 * Regular Expression callable for do_shortcode() for calling shortcode hook.
 * @see get_shortcode_regex for details of the match array contents.
 *
 * @since 2.5.0
 * @access private
 *
 * @global array $shortcode_tags
 *
 * @param array $m Regular expression match array
 * @return string|false False on failure.
 */
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, '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;
					}
				}
			}
		}
		$element = $front . implode( '', $attributes ) . $back;

		// Now encode any remaining [ or ] chars.
		$element = strtr( $element, $trans );
	}

	$content = implode( '', $textarr );

	return $content;
}

/**
 * Remove placeholders added by do_shortcodes_in_html_tags().
 *
 * @since 4.2.3
 *
 * @param string $content Content to search for placeholders.
 * @return string Content with placeholders removed.
 */
function unescape_invalid_shortcodes( $content ) {
        // Clean up entire string, avoids re-parsing HTML.
        $trans = array( '&#91;' => '[', '&#93;' => ']' );
        $content = strtr( $content, $trans );

        return $content;
}

/**
 * Retrieve the shortcode attributes regex.
 *
 * @since 4.4.0
 *
 * @return string The shortcode attribute regular expression
 */
function get_shortcode_atts_regex() {
	return '/([\w-]+)\s*=\s*"([^"]*)"(?:\s|$)|([\w-]+)\s*=\s*\'([^\']*)\'(?:\s|$)|([\w-]+)\s*=\s*([^\s\'"]+)(?:\s|$)|"([^"]*)"(?:\s|$)|\'([^\']*)\'(?:\s|$)|(\S+)(?:\s|$)/';
}

/**
 * Retrieve all attributes from the shortcodes tag.
 *
 * The attributes list has the attribute name as the key and the value of the
 * attribute as the value in the key/value pair. This allows for easier
 * retrieval of the attributes, since all attributes have to be known.
 *
 * @since 2.5.0
 *
 * @param string $text
 * @return array|string List of attribute values.
 *                      Returns empty array if trim( $text ) == '""'.
 *                      Returns empty string if trim( $text ) == ''.
 *                      All other matches are checked for not empty().
 */
function shortcode_parse_atts($text) {
	$atts = array();
	$pattern = get_shortcode_atts_regex();
	$text = preg_replace("/[\x{00a0}\x{200b}]+/u", " ", $text);
	if ( preg_match_all($pattern, $text, $match, PREG_SET_ORDER) ) {
		foreach ($match as $m) {
			if (!empty($m[1]))
				$atts[strtolower($m[1])] = stripcslashes($m[2]);
			elseif (!empty($m[3]))
				$atts[strtolower($m[3])] = stripcslashes($m[4]);
			elseif (!empty($m[5]))
				$atts[strtolower($m[5])] = stripcslashes($m[6]);
			elseif (isset($m[7]) && strlen($m[7]))
				$atts[] = stripcslashes($m[7]);
			elseif (isset($m[8]) && strlen($m[8]))
				$atts[] = stripcslashes($m[8]);
			elseif (isset($m[9]))
				$atts[] = stripcslashes($m[9]);
		}

		// Reject any unclosed HTML elements
		foreach( $atts as &$value ) {
			if ( false !== strpos( $value, '<' ) ) {
				if ( 1 !== preg_match( '/^[^<]*+(?:<[^>]*+>[^<]*+)*+$/', $value ) ) {
					$value = '';
				}
			}
		}
	} else {
		$atts = ltrim($text);
	}
	return $atts;
}

/**
 * Combine user attributes with known attributes and fill in defaults when needed.
 *
 * The pairs should be considered to be all of the attributes which are
 * supported by the caller and given as a list. The returned attributes will
 * only contain the attributes in the $pairs list.
 *
 * If the $atts list has unsupported attributes, then they will be ignored and
 * removed from the final returned list.
 *
 * @since 2.5.0
 *
 * @param array  $pairs     Entire list of supported attributes and their defaults.
 * @param array  $atts      User defined attributes in shortcode tag.
 * @param string $shortcode Optional. The name of the shortcode, provided for context to enable filtering
 * @return array Combined and filtered attribute list.
 */
function shortcode_atts( $pairs, $atts, $shortcode = '' ) {
	$atts = (array)$atts;
	$out = array();
	foreach ($pairs as $name => $default) {
		if ( array_key_exists($name, $atts) )
			$out[$name] = $atts[$name];
		else
			$out[$name] = $default;
	}
	/**
	 * Filters a shortcode's default attributes.
	 *
	 * If the third parameter of the shortcode_atts() function is present then this filter is available.
	 * The third parameter, $shortcode, is the name of the shortcode.
	 *
	 * @since 3.6.0
	 * @since 4.4.0 Added the `$shortcode` parameter.
	 *
	 * @param array  $out       The output array of shortcode attributes.
	 * @param array  $pairs     The supported attributes and their defaults.
	 * @param array  $atts      The user defined shortcode attributes.
	 * @param string $shortcode The shortcode name.
	 */
	if ( $shortcode ) {
		$out = apply_filters( "shortcode_atts_{$shortcode}", $out, $pairs, $atts, $shortcode );
	}

	return $out;
}

/**
 * Remove all shortcode tags from the given content.
 *
 * @since 2.5.0
 *
 * @global array $shortcode_tags
 *
 * @param string $content Content to remove shortcode tags.
 * @return string Content without shortcode tags.
 */
function strip_shortcodes( $content ) {
	global $shortcode_tags;

	if ( false === strpos( $content, '[' ) ) {
		return $content;
	}

	if (empty($shortcode_tags) || !is_array($shortcode_tags))
		return $content;

	// Find all registered tag names in $content.
	preg_match_all( '@\[([^<>&/\[\]\x00-\x20=]++)@', $content, $matches );

	$tags_to_remove = array_keys( $shortcode_tags );

	/**
	 * Filters the list of shortcode tags to remove from the content.
	 *
	 * @since 4.7.0
	 *
	 * @param array  $tag_array Array of shortcode tags to remove.
	 * @param string $content   Content shortcodes are being removed from.
	 */
	$tags_to_remove = apply_filters( 'strip_shortcodes_tagnames', $tags_to_remove, $content );

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

	if ( empty( $tagnames ) ) {
		return $content;
	}

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

	$pattern = get_shortcode_regex( $tagnames );
	$content = preg_replace_callback( "/$pattern/", 'strip_shortcode_tag', $content );

	// Always restore square braces so we don't break things like <!--[if IE ]>
	$content = unescape_invalid_shortcodes( $content );

	return $content;
}

/**
 * Strips a shortcode tag based on RegEx matches against post content.
 *
 * @since 3.3.0
 *
 * @param array $m RegEx matches against post content.
 * @return string|false The content stripped of the tag, otherwise false.
 */
function strip_shortcode_tag( $m ) {
	// allow [[foo]] syntax for escaping a tag
	if ( $m[1] == '[' && $m[6] == ']' ) {
		return substr($m[0], 1, -1);
	}

	return $m[1] . $m[6];
}