This class stores a set of bounds for characters or a single acceptable value, making it easy to define rule sets separately from the vocabulary defined for the examples.
Checks characters to see if they are part of the Name range - in XML 1.0, that's the combination of BaseChar, Ideographic, CombiningChar, and Extender.
Checks characters at the beginning of names against the range of acceptable NameStartChar characters, if there is one, and falls back on XML 1.0's Letter rules if there isn't.