null
XMl is not Aristotelian. It's fuzzy, and that's part of its
power and its usefulness
says Elliotte Rusty Harold. The assumption is that
validity is a boolean, i.e. either true or false, and that a
document cannot be both valid and invalid at the same time; and
furthermore that invalid documents are incorrect. In practice,
though, that's not what XML is about. X stands for Extensible.
[O'Reilly
Network] Agreed. Contrasting the differences
between validity and usefulness is the point of
this essay.