The somewhat strained tone in this definition evidences the somewhat strained quality of debate that created it. The problem is simple. Being compatible with SGML is a real virtue, for several reasons:
On the other hand, SGML was designed in the early-to-mid 1980s, and with experience, we have come to be keenly aware of some design errors. It was very tempting merely to eliminate them from XML, and some of us thought that this was the way to go. Eventually, we decided to include some rather questionable constraints on XML simply for the sake of compatibility.
One of the reasons why this was easy was the eagerness of the SGML community to work with us, and in fact to modify SGML to remove some of these irritants, to an extent that was very gratifying.
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