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In almost all places where the CLI/deps reference uses :aliases it means the literal key :aliases in the deps.edn file.
In two places -- -X[:aliases] and -M[:aliases] -- it means instead a list of aliases.
I think removing the : in those two cases would be more consistent with the other uses of the word "aliases" in the text (as opposed to the _keyword :aliases).
Seems reasonable. That's actually pulled from clj -h though so need to consider how to sync those up. clj man page uses slightly different syntax like -X[:alias...].