CreatePartsFromList fails to account for the hypothetical reality of 3-item templates admissible by Unicode

[dead-claudia]

In https://www.unicode.org/reports/tr35/tr35-general.html#ListPatterns, there's a direct reference to an optional 3-element pattern that may exist, working similarly to 2-element patterns. I'm not currently aware of languages that use it, but it is in theory possible, and the spec should use it.

Edit: relevant spec link: https://tc39.es/ecma402/#sec-createpartsfromlist