Major There are some issues and ambiguities in how we represent the request in the ContextUrl.
1) From 10.9, "If the context URL includes only expanded navigation properties (i.e., only navigation properties suffixed with parentheses), then all structural properties are implicitly selected (same as if there were no properties listed in the select-list)."
As a result, there is no way to say that a result contains only the expanded content and no selected properties. This is not a huge issue, as our syntax today doesn't allow requesting only expanded properties, but it seems like it should.
2) In 4.01 we say that, for expanded navigation properties with no expand options, the context URL contains the name of the navigation property suffixed with empty parens, and that this MAY be omitted in 4.0. However, the 4.0 grammar prohibits the use of empty parens.