code: function sourceString(source) {
    var message = "<css input>"
    if (source) {
      if (source.input && source.input.file) {
        message = source.input.file
      }
      if (source.start) {
        message += ":" + source.start.line + ":" + source.start.column
      }
    }
  
    return message
  }
docs: Returns GNU style source
  
  @param {Object} source