text: """
  Package for filter expressions which operate on a particular field
  of a model.
  """
  from ._Compare import Compare
  from ._Contains import Contains
  from ._Exact import Exact
  from ._FieldFilterExpression import FieldFilterExpression
  from ._IsNull import IsNull
  
  # The set of all concrete field filter-expressions
  ALL_FIELD_FILTER_EXPRESSIONS = frozenset((Compare, Contains, Exact, IsNull))
  