markFeatureWriter: RightToLeft lookupflag emitted on lookups that cannot honor it (types 4/5/6)

[pauldhunt]

Observed on main @ 56401be (fetched 2026-07-28), in make_lookup_wrappers (lines 617–638).

Behavior

make_lookup_wrappers appends _RightToLeft_ to the lookup flag whenever the anchor name ends in AR, HE, or RTL:

rtl = anchor_name.endswith(('AR', 'HE', 'RTL'))
lookup_flag = ['lookupflag']
if rtl:
    lookup_flag.append('RightToLeft')

Per the OpenType specification, the RightToLeft lookup flag (0x0001) is honored only by GPOS lookup type 3 (cursive attachment). The lookups this script emits are MARK_BASE_* (type 4), MARK_LIGATURE_* (type 5), and MKMK_MARK_* (type 6). The string cursive does not appear anywhere in the file, so no type-3 lookup is ever produced.

Every RightToLeft the script emits therefore has no effect at shaping time. It compiles cleanly and is inert.

Question

Is this intentional (e.g. forward-compatibility, or parity with hand-authored RTL feature conventions), or is the flag
safe to drop on the non-cursive lookups this script emits?

[behdad]

Safe to drop.