do_shortcodes_in_html_tags( string $content, bool $ignore_html, array $tagnames )

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;
}