This message is generated when a rule is not found for an expression in the indicated format and ParentForm for that format is not found in the value of $BoxForms.
Off[message] switches off the message; On[message] switches it on. For example: Off[ParentForm::deflt].
范例
基本范例(1)
ParentForm for the indicated format has not been defined:
This shows a valid ParentForm specification for the new format:
