code: function getCompoundFileExtension(fullPath) {
          var baseName = FileUtils.getBaseName(fullPath),
              parts = baseName.split(".");
  
          // get rid of file name
          parts.shift();
          if (baseName[0] === ".") {
              // if starts with a `.`, then still consider it as file name
              parts.shift();
          }
  
          var extension = [parts.pop()], // last part is always an extension
              i = parts.length;
          while (i--) {
              if (getLanguageForExtension(parts[i])) {
                  extension.unshift(parts[i]);
              } else {
                  break;
              }
          }
          return extension.join(".");
      }
docs: Get the file extension (excluding ".") given a path OR a bare filename.
  Returns "" for names with no extension.
  If the only `.` in the file is the first character,
  returns "" as this is not considered an extension.
  This method considers known extensions which include `.` in them.
  
  @param {string} fullPath full path to a file or directory
  @return {string} Returns the extension of a filename or empty string if
  the argument is a directory or a filename with no extension