Of course a standard which mandates space folding is also
within its rights to mandate, for example, the non-use of
nonspacing marks applied to SPACE characters. It can simply
rule out such sequences as valid for its context, in which
case the problem goes away.
And for such standards or applications one can usually use U+00A0 NO-BREAK SPACE to force multiple spacings.
One can also use this followed by a non-spacing combining character to call for rendering of that combining character in isolation.
My feeling is that because of the special qualities of regular SPACE using NBSP (U+00A0) should be the more robust way to go.
Essentially, since the Unicode specifications say that a non-spacing diacritic can be applied to any base character, including the spaces, it is up to fonts and other presentation software to support this and to try to make the results look good according to othrographic and cultural expectations, just as it is with any text coded in Unicode.
Sometimes fonts don't do this. I would not at all be surprised to find for example that _g_ followed by U+0325 COMBINING RING BELOW would come out with the combining ring overlapping the tail of the _g_ unless I were using a font especially designed for linguistic use.
I would not be at all surprised that some fonts and display devices wouldn't justify NBSP + COMBINING DOT BELOW at the beginning of a line. But good typographical fonts should justify such combinations and should presumably change the width of NBSP when appropriate.
Such changes of width and shapes are what one finds with ligatures in fonts that support ligatures.
Jim Allan
