This adds a bit more inconsistency to the library, but we didn't have complete consistency before. Almost all existing string enum values are lowercase (a couple are camelCase and one is dash-separated). The closure library isn't consistent either (with case for enum properties or values). I imagine this could be justified in saying someone could blindly use GeoJSON type values in places, but in the end, you'll need to read the docs before guessing right.
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