+selects only bytes 264..1263 from the original object. As an
+abbreviation, the slice syntax
+ [<length>]
+is shorthand for
+ [0+<length>]
+In place of a traditional slice, the annotation
+ [=<length>]
+may be used. This is somewhat similar to specifying [<length>], but
+additionally asserts that the referenced object is exactly <length>
+bytes long--that is, this slice syntax does not change the bytes
+returned at all, but can be used to provide information about the
+underlying object store.