And by no means, in my opinion, should this debugging
facility be a part of the language.
The debugging facility is not part of the language. What the language
does is to enable a stylesheet to make assertions about its input and
output. It's normal good software engineering that programs should
declare their expectations about their input and output. Without such
assertions, there is no bug if the expectations are not satisfied, and
therefore no debugging is possible.
Michael Kay
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