docs: def parse_permission_set(input):
      """Lookup a permission set name in the defined permissions.
  
      Requires a Flask app context.
  
      """
  
      # Priority goes to the user's parsers.
      if isinstance(input, basestring):
          for func in current_acl_manager.permission_set_parsers:
              res = func(input)
              if res is not None:
                  input = res
                  break
  
      if isinstance(input, basestring):
          try:
              return current_acl_manager.permission_sets[input]
          except KeyError:
              raise ValueError('unknown permission set %r' % input)
  
      return input