If I reverse engineered a DTD, would my chances of earning my XML repair badge be better?
Maybe. That will depend on the DTD. But how do you know that what you reverse engineer is correct? Or perhaps you reverse engineer a DTD (which may, or may not) be correct, and allows non-ambigious repairs. (That's not so far-fetched. Consider an HTML or XHTML document with the some of the </EM> tags missing. It will not always be clear where to insert the missing tags, even if you assume they belong just before or after some other tag).
One disadvantage of attempting to repair, and not knowing how to recognize a correct document, is that you may end up with a document that is well-formed, or even conforming to the DTD you have, or reversed engineered, is that you do not know whether you ended up with the right document.
Consider a Perl program of which a quote is missing. You could write a "repair" program that noticed a quote is missing, and puts a quote back into the program. Now, if you just randomly inserted the quote in the program, you're likely to end up with a program that still doesn't compile. But for most programs that are missing a quote, there will be more than one place the quote can be inserted, and you still have a compilable program. Which one should your repair program pick? How does it now it's right?
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