John Cowan wrote:

> Marco Cimarosti scripsit:
> > [...]
> > Visual-order [...] also needs the reverse function,
> > to generate a "back store" from a "visual store"
>
> In fact both methods generally need both functions, in order
> to determine what's being clicked on correctly.

Not necessarily: each glyph in the "visual store" could contain (a)
pointer(s) to the character(s) in the "back store" to which it maps.

--
Marco