... 0xd800 is not a legal XML character....
<high-unicode ...>𐀀</high-unicode>
Now: whose problem is this Slide's or JDOM's?
JDOM, I'd guess without looking at the code. This is a very general problem: The surrogate Unicode codepoints are illegal for itself in XML, but of course in Java strings there is no way to express non-baseplane characters other than as two surrogates. Problem: if the test for illegal surrogates is before character reference expansion, illegal surrogates may sneak in as char refs. If the test is after character reference expansion, a non-baseplane character may trigger a false positive. Obviously, the test has to be done twice, once for literal characters and once as part of dealing with character references.
I personally wouldn't loose much sleep over this particular problem. Unless you are into MathML or obscure historic scripts, non-baseplane characters are more of a curiosum.
J.Pietschmann
