I am not a font professional -- using an existing font and trying to map a Unicode range to another (Syriac font, the Hebrew Unicode points mapped to Syriac glyphs).
In FontForge, for each Hebrew alphabet Unicode point, I add an "Alternate Unicode Encoding" in Glyph Info > Unicode and the previously empty Unicode points now display the correct glyphs.
The problem is, the Substitutions are not applied, i.e. ligatures between adjacent glyphs etc. They are correctly applied when the original Unicode points of the glyphs are entered, but not the new "alternate encoding" (Hebrew) Unicode points.
Am I doing something wrong? I thought these Substitutions depended on glyphs, not Unicode points, so not sure why it doesn't work.