[HarfBuzz] Backspace and Delete behaviours

[Behdad Esfahbod]

On 07/23/11 12:06, Rajeev J Sebastian wrote:
> whereas backspace erases logical characters.

This is vague and wrong.  What's a logical character?  If you simply mean
Unicode character, then there's a trivial reason for why this is wrong:
ideally user shouldn't know or care about the difference between NFC and NFD.
 Backspace, delete, cursor movement, all should ideally work the same with
NFC, NFD, or any other canonically equivalent Unicode text.

And, one size does not fit all.  For example, Arabic non-spacing marks are
vowel marks that one would expect to be able to back-space, but say, grave
accent, or any of the other Latin marks, are diacritic marks, not vowels.
They simply _modify_ their base, so user expects backspace to delete the mark
and the base.

This discussion is more appropriate for the Pango mailing list at this point.
 In pango it is my plan to add a specific language-module API for backspacing
and let customize per script / language.

behdad