docs: def validate_variable_name(self, name):
          """
          Validate variable name.
  
          Arguments:
              name (string): Property name.
  
          Returns:
              bool: ``True`` if variable name is valid.
          """
          if not name:
              raise SerializerError("Variable name is empty".format(name))
  
          if name[0] not in PROPERTY_ALLOWED_START:
              msg = "Variable name '{}' must starts with a letter"
              raise SerializerError(msg.format(name))
  
          for item in name:
              if item not in PROPERTY_ALLOWED_CHARS:
                  msg = ("Invalid variable name '{}': it must only contains "
                         "letters, numbers and '_' character")
                  raise SerializerError(msg.format(name))
  
          return True