Bengali অ্যা and এ্যা [æ] are treated as a single grapheme for letter-spacing.

[r12a]

Test link(s):

test

Results:

The test was run with the following pre-installed fonts:
Windows: Shonar Bangla, Arial Unicode MS, Nirmala UI, Vrinda
Mac: Bangla MN, Bangla Sangam MN, Kohinoor Bangla, Tiro Bangla, Baloo Da
Also tested with Noto Sans Bengali and Noto Serif Bengali on the Mac.

• Gecko: ✅❌ Windows: works with all fonts. Mac: fails with Bangla MN, Bangla Sangam MN, and Baloo Da, but works with the others. Works with Noto fonts. Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:95.0) Gecko/20100101 Firefox/95.0
• Blink: ✅❌ Windows: works with all fonts. Mac: same results as for Gecko. Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.93 Safari/537.36
• Webkit: ❌ Mac: failed for all fonts. In fact, letters were all spaced individually, rather than by grapheme cluster. Could not apply Noto fonts. Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.1 Safari/605.1.15

Related tests: Letter spacing