Rerouted (regenerated, verified). Same repository and tag, but GitHub now builds the zip with different bytes, so it no longer matches the SHA-1 package.elm-lang.org recorded. The Lamdera package server serves a copy recovered from https://github.com/jxxcarlson/elm-l0-parser.
What we checked: Tag 1.2.2 is still on github.com/jxxcarlson/elm-l0-parser; its commit 6073124b189c is from 2021-12-10 00:52 UTC, before the version was published (2021-12-10 00:53 UTC); elm.json is byte-identical to package.elm-lang.org's; the exposed modules match docs.json; the zip's SHA-1 is not the published one (GitHub's zip no longer comes out byte for byte the same), so the contents were checked instead.
The Lamdera compiler uses this copy and prints a one-line notice saying so. elm itself fails to download this version.
Details · package.elm-lang.org's zip: https://github.com/jxxcarlson/elm-l0-parser/zipball/1.2.2/
A Parser for the experimental L0 module. See the app folder to see how it is used. The Render folder in app could have been included with the parser. However, this way users are free to design their own renderer.
Since this package is still experimental (but needed in various test projects). The documentation is skimpy.