[^\;\}]*))?' .
			self::URL_REGEX . '(?P[^;]*)[\;]?/';
		$offset = 0;
		while ( preg_match( $pattern, $source, $match, PREG_OFFSET_CAPTURE, $offset ) ) {
			// Shortcuts
			$embed = $match['embed'][0];
			$pre = $match['pre'][0];
			$post = $match['post'][0];
			$file = "{$local}/{$match['file'][0]}";
			$url = "{$remote}/{$match['file'][0]}";
			// Only proceed if we can access the file
			if ( file_exists( $file ) ) {
				// Add version parameter as a time-stamp in ISO 8601 format,
				// using Z for the timezone, meaning GMT
				$url .= '?' . gmdate( 'Y-m-d\TH:i:s\Z', round( filemtime( $file ), -2 ) );
				// If we the mime-type can't be determined, no embedding will take place
				$type = false;
				$realpath = realpath( $file );
				// Try a couple of different ways to get the mime-type of a file,
				// in order of preference
				if ( $realpath
					&& function_exists( 'finfo_file' ) && function_exists( 'finfo_open' )
					&& defined( 'FILEINFO_MIME_TYPE' ) )
				{
					// As of PHP 5.3, this is how you get the mime-type of a file;
					// it uses the Fileinfo PECL extension
					$type = finfo_file( finfo_open( FILEINFO_MIME_TYPE ), $realpath );
				} else if ( function_exists( 'mime_content_type' ) ) {
					// Before this was deprecated in PHP 5.3,
					// this used to be how you get the mime-type of a file
					$type = mime_content_type( $file );
				} else {
					// Worst-case scenario has happened,
					// use the file extension to infer the mime-type
					$ext = strtolower( pathinfo( $file, PATHINFO_EXTENSION ) );
					if ( isset( self::$mimeTypes[$ext] ) ) {
						$type = self::$mimeTypes[$ext];
					}
				}
				// Detect when URLs were preceeded with embed tags,
				// and also verify file size is below the limit
				if ( $embed && $type && $match['embed'][1] > 0
					&& filesize( $file ) < self::EMBED_SIZE_LIMIT )
				{
					// Strip off any trailing = symbols (makes browsers freak out)
					$data = base64_encode( file_get_contents( $file ) );
					// Build 2 CSS properties; one which uses a base64 encoded data URI
					// in place of the @embed comment to try and retain line-number integrity,
					// and the other with a remapped an versioned URL and an Internet Explorer
					// hack making it ignored in all browsers that support data URIs
					$replacement = "{$pre}url(data:{$type};base64,{$data}){$post};";
					$replacement .= "{$pre}url({$url}){$post}!ie;";
				} else {
					// Build a CSS property with a remapped and versioned URL,
					// preserving comment for debug mode
					$replacement = "{$embed}{$pre}url({$url}){$post};";
				}

				// Perform replacement on the source
				$source = substr_replace( $source,
					$replacement, $match[0][1], strlen( $match[0][0] ) );
				// Move the offset to the end of the replacement in the source
				$offset = $match[0][1] + strlen( $replacement );
				continue;
			}
			// Move the offset to the end of the match, leaving it alone
			$offset = $match[0][1] + strlen( $match[0][0] );
		}
		return $source;
	}
	
	/**
	 * Removes whitespace from CSS data
	 *
	 * @param $css string CSS data to minify
	 * @return string Minified CSS data
	 */
	public static function minify( $css ) {
		return trim(
			str_replace(
				array( '; ', ': ', ' {', '{ ', ', ', '} ', ';}' ),
				array( ';', ':', '{', '{', ',', '}', '}' ),
				preg_replace( array( '/\s+/', '/\/\*.*?\*\//s' ), array( ' ', '' ), $css )
			)
		);
	}
}