Unicode restriction

In src/backend/utils/mb/wchar.c there is a check to exclude Unicode
characters above 0x10000. I can't see anything to explain this
restriction, except possibly this in the release notes for 7.2:

Reject invalid multibyte character sequences (Tatsuo)

It does not explain why part of the Unicode character range is invalid.
There is a Debian bug report from someone whose client is trying to
store characters in the excluded range. What would be needed to enable
support for it?

--
Oliver Elphick olly(at)lfix(dot)co(dot)uk
Isle of Wight http://www.lfix.co.uk/oliver
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