This module implements an object class, instances of which store a
(mutable) string buffer that supports tags. A tag is a name/value pair that
applies to some non-empty extent of the underlying string.

The types of tag names ought to be strings, or at least values that are
well-behaved as strings, as the names will often be used as the keys in
hashes or applied to the 'eq' operator.

The types of tag values are not restricted - any scalar will do. This could
be a simple integer or string, ARRAY or HASH reference, or even a CODE
reference containing an event handler of some kind.