docs: def attr_string(filterKeys=(), filterValues=(), **kwargs):
      """Build a string consisting of 'key=value' substrings for each keyword
      argument in :kwargs:
  
      @param filterKeys: list of key names to ignore
      @param filterValues: list of values to ignore (e.g. None will ignore all
                           key=value pairs that has that value.
      """
      return ', '.join([str(k)+'='+repr(v) for k, v in kwargs.items()
                        if k not in filterKeys and v not in filterValues])