Each character's initial/medial/final/isolated GSUB form is resolved from its own Unicode Joining_Type, not rendered as an unjoined isolated glyph - the same shaping a browser applies.
بيت ("house", Beh-Yeh-Teh) - each letter takes its own initial/medial/final connected form:
بيت
The same dual-joining letter (Beh) repeated once, twice, and three times in a row forces isolated, then initial+final, then initial+medial+final forms of the identical character - the standard way to demonstrate all four forms unambiguously:
| Isolated | Initial + Final | Initial + Medial + Final |
|---|---|---|
| ب | بب | ببب |
rlig)لا ("no", Lam-Alef) - a font's own required ligature connects the two letters into one glyph. This needs shaping to run in true logical (Lam-then-Alef) order even though the word displays right-to-left - reversing the source text before shaping (as a naive implementation might) would prevent this exact ligature rule from ever matching.
لا
curs)A calligraphic font ("Aref Ruqaa") whose flowing baseline connections rely on GPOS cursive attachment, not only positional substitution - each letter's own exit/entry anchor points connect edge to edge:
بيتالف