Do not mix Unicode and traditional strings in indexes or SortedCollections
Unicode strings (Unicode7, Unicode16, and Unicode32) and traditional strings
(String, DoubleByteString, and QuadByteString), have different comparison
code, and the ordering of a mixed collection is not consistent. You should
not mix these types of strings in an indexed collection, or a SortedCollection,
since lookups may fail.
In v3.2, mixing these has been disallowed and other options are provided
to create usable orderings.
Last updated: 5/7/14