Updated code documentation

Allows generating a proper documentation using JSDuck.
(A custom JSDuck tag class for "licence" tag should be applied upon generation.)
Logically, you are right and I had the same thinking when writing the initial documentation. However, technically, it is wrong and the JSDuck parser complains about that. You cannot have a required attribute after an optional attribute. Anyway, I will correct the documentation since the languageCode param may also be a MultiTermMap.