code: def _call_shallow_validation(self, value):
      
      methods = []
      for method in self._find_methods('_validate', '_to_base_type'):
        if method.__name__ != '_validate':
          break
        methods.append(method)
      call = self._apply_list(methods)
      return call(value)
docs: Call the initial set of _validate() methods.
  
      This is similar to _call_to_base_type() except it only calls
      those _validate() methods that can be called without needing to
      call _to_base_type().
  
      An example: suppose the class hierarchy is A -> B -> C ->
      Property, and suppose A defines _validate() only, but B and C
      define _validate() and _to_base_type().  The full list of
      methods called by _call_to_base_type() is::
  
        A._validate()
        B._validate()
        B._to_base_type()
        C._validate()
        C._to_base_type()
  
      This method will call A._validate() and B._validate() but not the
      others.