#5 Deal with bad tag names or attr names.

[Eamonn O'Brien-Strain]

It is possible to create a DOM in memory with bad
element tag names or attribute names. For example they
could contain whitespace, '=', '<' or '>'. We should
do one of three things:

(1) Do not change the code but document the
preconditions of what the strings should contain.

(2) Move the checking code from the parser to the DOM
creating code.

(3) "Encode" bad tag and attribute names as correct
names, either on creation or when doing a toXml()
serialization.