docs: def taint(taintedSet, taintedAttribute):
      u"""Adds an attribute to a set of attributes.
  
      Related attributes are also included."""
      taintedSet.add(taintedAttribute)
      if taintedAttribute == 'marker':
          taintedSet |= set(['marker-start', 'marker-mid', 'marker-end'])
      if taintedAttribute in ['marker-start', 'marker-mid', 'marker-end']:
          taintedSet.add('marker')
      return taintedSet