a character for an unknown character

[Richard Wordingham]

On Wed, 21 Dec 2016 02:29:59 +0000
Martin Mueller <martinmueller at northwestern.edu> wrote:

> I’m new to this list. Please excuse my technical incompetence.
> Is there a Unicode character that says “I represent an alphanumerical
> character, but I don’t know which”.  This is a very common problem in
> the transcription of historical texts where you have lacunas. Often,
> the extent of the lacuna is known, and the alphabet is known as well.

U+FFFD REPLACEMENT CHARACTER says that one can't represent (or
interpret) the specified character as Unicode.

U+3013 GETA MARK says the character isn't encoded, and I suspect
implies not being available as a usable PUA character.

U+0359 COMBINING ASTERISK BELOW can mean that we have to take someone's
word for what the character is - he claimed he knew, but we can't see
the evidence.  (That is the meaning given when the character was
added, but it can have other meanings - I've seen a Thai dictionary
use it as a nukta.) 

The concept here is 'no-one in communication knows for sure what the
character is'.  The usual notation for this is diagonal shading, for
which CSS mark-up repeating-linear-gradient is now available.
Graphically, the best character, which may not be considered completely
appropriate, is

U+26C6 RAIN

Having a general class of symbol_other, just like U+3013, it should
have the appropriate Unicode properties.  I'm just not sure that one
can justify it as 'something washed the character out' -:)  Script
should only matter if there is a known combining character, in which
case we are heading for the territory of partial damage marks, which
generally feel like mark-up.

If we add a bespoke character, it might belong in a punctuation block,
just as u+3013 does.  It represents a gap, like SPACE, but this time,
generally a hole in the medium of the text.

Richard.