code: def is_valid_varname(self, name, item):
          
          check_valid_varname(name, self._custom_units, self._structs, self._constants, item)
          if name in self._globals:
              raise VariableDeclarationException(
                  'Invalid name "%s", previously defined as global.' % name, item
              )
          return True
docs: Valid variable name, checked against global context.