Thawable and Freezable interfaces, whose purpose is to give meaning to the idea of dynamic optional methods.
Added missing GPL headers.
Moving to Java 8 required tweaking some annotations.
Utility classes.
Efficiency tweaks.
Added comments.
Java 8 makes _ a reserved word, so have to rename it.
Added GPL header.
Got rid of alternative field suffix. Also added GPL header.
Added copy constructor and shallow & deep copying.
Much more rigorous on sharing. Introduced the 'quick' as-map conversion for efficiency.
Added the incremental iterator - a pre-order walk, with options for depth v breath first & forward & reverse.
Added missing test classes.