3.1.1 Static context
under statEnv.collectionType it says "It [The collection types 
environment] contains the static type for the input collections...". 
This sentence suggests that there is a single type for all 
collections, which is belied by the later and more accurate 
statement that "The collection types contain bindings from input 
URIs (a URI) to types (a Type).".  The first sentence should make 
the word "type" plural ("types"), or, for maximum clarity, you 
should use a universal quantifier: "It contains, for each 
statically-known collection, the static type of that collection".  
The first sentence under statEnv.docType
has the same problem and the same fix.