json-ld/json-ld.org — comment on commit 9183ee00ac97358ef20477446619580c8b9aae8d
File: spec/latest/json-ld-syntax/index.html line 582
By lanthaler:

Till this point in the document there wasn't any mention about prefix:suffixes. That's an advanced topic. I thus find it very confusing to talk about empty terms in this context. On the other hand, in the Prefixes section it is clearly described that prefixes and suffixes can be empty strings.