'Return extensions that has the given tag and belongs to the
given schema as native elements of that schema.
:param tag: The tag of the element
:param schema: Which schema the element should originate from
:return: a list of native elements'

def extensions_as_elements(self, tag, schema):

    result = []
    for ext in self.find_extensions(tag, schema.NAMESPACE):
        ets = schema.ELEMENT_FROM_STRING[tag]
        result.append(ets(ext.to_string()))
    return result
