Even in the first position? That makes it no longer be the claimed "superset of JSON", since (AFAIK) {"key":"value"} (with no whitespace) is valid JSON.
For delimited collections, so within {} and [], if the key is quoted, then you don't need the whitespace. So your example parses as expected as does `{"key":value}`, but `{key:value}` turns into `{"key:value": null}`.
This is incorrect. The colon needs to be followed by whitespace for it to indicate a key-value pair. You can check this with the reference parser (and a bunch of others!) online: https://play.yaml.io/main/parser?input=YWxsb3dlZC1pcHM6IFswL...