Hans,

Thank you for your suggestion. I tried disabling all otf features except besub, but it didn't work. I presume that prepend should be added like this:

\startluacode
fonts.handlers.otf.addfeature {
name = "besub",
type = "substitution",
prepend = true,
data = {
["uni0431"] = "uni0431.SRB.alt"
}
}
\stopluacode

BTW, I'm using LMTX Context version 2022.01.21 20:13. Should I send you some files for diagnostics?

On Wed, Feb 23, 2022 at 12:00 AM Hans Hagen via ntg-context <ntg-context@ntg.nl> wrote:
On 2/19/2022 4:59 PM, Stefan Nedeljkovic via ntg-context wrote:
> Dear list,
>
> I'm using the typeface Neacademia Text, and I'm trying to configure it
> to the specifics of the Serbian language. I want to replace the usual
> form of the lowercase cyrillic letter BE with the traditional Serbian
> form. I opened the font file in Font Forge and looked up the glyph info.
> Here is what I tried and what failed:
>
> \startluacode
> fonts.handlers.otf.addfeature {
> name = "besub",
> type = "substitution",
> data = {
> ["uni0431"] = "uni0431.SRB.alt"
> }
> }
> \stopluacode
>
> \definefontfeature[default]
>    [mode=node,kern=yes,
>    liga=yes,dlig=yes,
>    calt=yes,ss03=yes,
>    case=yes,ccmp=yes,
>    locl=yes,script=cyrl,language=srb,
>    besub=yes]
>
> No luck using hex codes either:
>
> \startluacode
> fonts.handlers.otf.addfeature {
> name = "besub",
> type = "substitution",
> data = {
> [0x1ab] = 0x3f8
> }
> }
> \stopluacode"uni0431"
>
> Interestingly the single substitutions from page 175 of the fonts manual
> seem to work just fine.
> Any help is appreciated.
hard to say but you enabel quite some features so probably uni0431 is
already replaced .. maybe

     prepend = true,

helps

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