form feed not allowed in XML

[Patrice Dumas]

Hello,

Form-feed is siply forbidden in XML.  In text it is not a problem, as
elements may be used.  In attributes, however, I found no possibility to
escape simply form-feed.  Even using xml 1.1 explictely does not change
the problem, although it is claimed that it should, for instance on
https://en.wikipedia.org/wiki/Numeric_character_reference#Restrictions

So, in attributes, I output a literal \f (two characters, antislash and
f) and I protect \ by doubling it.

If there is a better way, I'd be happy to use it.

Maybe this should be documented?

in spaces and trailingspaces attributes, similarly, a eol is \n 
(antislash and n) and a formfeed is \f (two characters, antislash and f).
but it is not problematic in this context, as there should only be
spaces together with \n and \f in this context.

-- 
Pat