Den 2015-05-22 21:14, David M. Jones skrev:
Arguably, it never is -- if you want a dotted circle, you can add it
yourself, whereas it's not at all unusual to want to show combining
marks in isolation in, say, textbooks.
Showing it with a dotted circle as stand in for a base character,
whether automatically inserted (which I wouldn't like) or with an
explicit U+25CC is the correct way to show a combining character
in such a case, since it shows clearly where the combining mark
would be in relation to the base character. You can always add a
footnote to the effect that ◌ is conventionally used in place of a
base character when discussing a combining mark without reference
to a base character.
Even if you want the mark to 'hang in the air' a combining mark
needs something with width to 'hang' it on even in that case, and
a nonbreaking space would seem to be the natural choice. If you
(likely) need finer control over spacing one or more of the
characters in the U+2000...U+200A range may serve, but remember
that the visual effect may be font dependent.
FWIW I checked some lead-printed Sanskrit grammars and
dictionaries and they all use some base character (क or त in all
cases) when discussing combining marks; there simply weren't any
type for marks without a base character. Compared to that the
dotted circle is a huge advance! Especially in a table it makes
the difference between superscript, subscript and superimposed
marks immediately clear.
Alas U+25CC seldom is equipped with the anchors necessary to
display marks correctly in relation to it, if there is a glyph for
it at all. Often you need to use another font and adjust the size
of the dotted circle itself.
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