.function {greet}
.greet {world} from:{iamgio}
I strongly suggest that the greet call uses a slightly different syntax (e.g. two dots) as the system otherwise can't introduce new keywords without risking conflict with function names in existing documents.A backward compatible design would be resolve to user-defined functions first, built-in keywords afterwards.
That way any new keywords won't be a backward incompatible change.
Does it need more keywords? This syntax reminds me of Smalltalk syntax a little and Smalltalk famously got away with merely 6 keywords. I didn't check the syntax in detail for quarkdown, and I don't expect it to be as well thought out as Smalltalk, but it is quite possible to get away with only few keywords. Question is then how complete their concept is right now. Also there could be a versioning mechanism, that labels a document as for a specific version of Quarkdown.