A Friday afternoon XML koan

There are many aspects of XML that require knowledge of its context. For example, earlier in the week my "XML quiz" noted that & does not always mean & (in the context of a CDATA section or a comment it means & but otherwise it means &)

So things are context-dependent.

Another way of saying it is: Things are context-sensitive. XML is context-sensitive.

Koan: If XML isn't context-free, why are we always writing context-free grammars for it?  (And don't say, "Because it's useful to do so;" that begs the question:  Why is it useful?)

Scroll down to see the answer ..............




















Even though XML isn't context-free as such, it is locally context-free, in the sense that the set of permissible expressions within a small region in a particular XML document can be described by a context-free grammar.

Adapted from the article "The Concept of Grammar Adaptability" by John N. Shutt (https://web.cs.wpi.edu/~jshutt/adapt/concept.html)