[Groff] unicode support - where to compose?

[Bruno Haible]

Hi,

When an input file contains the character <U+1EBF>, preconv transforms it
to \[u1EBF], and troff transforms it to a single glyph u0065_0302_0301. Fine.

But when an input file contains the characters <U+0078><U+0302><U+0301>,
preconv transforms it to x\[u0302]\[u0301], and troff produces three distinct
glyphs x, u0302, u0301. This is wrong. But should the composition be
handled within preconv or within troff? In other words, what should happen
if the input file contains

               x\[u0302]\[u0301]  ?

Is groff allowed to combine these three input nodes into a single one? Or
is there some principle in the groff input language that would force groff
to consider these as three different units?

In the first case I would put the composition into troff. In the second
case into preconv (i.e. preconv would translate <U+0078><U+0302><U+0301> to
\[x u0302 u0301] but would leave alone x\[u0302]\[u0301]).

Bruno