12:22
<hsivonen>
sffc: Did you overlook this line: https://github.com/unicode-org/cldr/blob/9931b3281c82cf82f267c12d732f4e207fd4bff3/common/supplemental/supplementalData.xml#L4869 ? Anyway, as I asked on the ICU4X issue: What does islamic in CLDR data really mean: Does it mean the behavior in ICU4C or does it mean more generally that a local-to-region observation is used or something else? FWIW, https://web.archive.org/web/20170508214424/http://www.moonsighting.com/calculation-or-sighting.html from 2016 does not match CLDR.
12:26
<hsivonen>
I think it would be a good exercise to try to write an MDN explanation for what islamic does and when one would use it instead of islamic-umalqura, islamic-civil, or islamic-tbla.