code: def _process_schema(self, schema_dict, validators):
          
          schema_flat = util.flatten(schema_dict)
  
          for key, expression in schema_flat.items():
              try:
                  schema_flat[key] = syntax.parse(expression, validators)
              except SyntaxError as e:
                  # Tack on some more context and rethrow.
                  error = str(e) + ' at node \'%s\'' % key
                  raise SyntaxError(error)
          return schema_flat
docs: Go through a schema and construct validators.