3.1.1 Static context
It says "Environments have an initial state when [expression/query] 
processing begins, containing, for example, the function signatures of 
all built-in functions".  True, but isn't the model that an environment
(or probably more appropriately, an environment group) is invariant?
Saying that it has an initial state gives the impression that this state
may change, whereas the model is to create a whole new environment group
to reflect any evolution in the environment group.
In that case, it would be better to say that there is an initial 
environment group.