'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.'

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)
