In these products, parsing for the instance is internal to the product. DTD-centric parsing is done in batch. That may not be the solution people want, but it is one way. Well-formedness also has precedents in Xerox systems of the period. T'is new to thee, Miranda.
Full validation is the only option.
I do want to be able to use SGML techniques that worked in the past and still work sensibly. Validation can be switched on or off by the 'client'. This is the best approach if the flag is clear to all. Undocumented at present.