The classes described in this branch are seldom used in the client code directly. First of all, they serve as building blocks for the top-level data structures. Among them there are, however, several constructions that can be useful also separately from these top-level classes.

### Container manipulations

Simple operations on containers yielding another container-like objects, such as element selection, transformation, etc. Allow to extend easily the functionality of algorithm templates expecting their input in STL-conforming containers.

### Advanced container features

How to make standard containers and iterators to offer a little bit more than they had used to.

### Union classes

Type-safe analogs to the classical C union.

### Operations

STL-conform functors (and more) allowing to wrap the built-in and overloaded operators into functional-style expressions.

### to be continued...