[XeTeX] Whitespace in input

[Philip TAYLOR]

Zdenek Wagner wrote:

> If you know what such characters are (and it will certainly be
> documented), you just set their categories back to 12 in order to get
> the old behaviour.

No ! "A catcode is for life, not just for Christmas" !  Once a
character has been read, and bound into a character/catcode pair,
that catcode remains immutable.  That means that code that is /not/
expecting to have to deal with non-standard catcodes could none the
less be passed token lists containing such entities if it is
possible, within a document, to turn such a feature on and
off again.

** Phil.