Restricted String value class would be useful - limit length, characters, etc.

[lisad]

String values are sometimes subject to constraints that aren't appropriate to the other kinds of data types

• Forbidden characters: characters like '<', '$', '%' may be forbidden in fields like name, title
• Instead of a forbidden list, the datatype might only have allowed characters e.g. (a-zA-Z) or a class of allowed characters and others are forbidden. (what does pandas do here if anything?
• Strings may have minimum character length or maximum

Although a plain Column is fine for strings without these constraints, should we make a ConstrainedString or RestrictedString column type that has these constraints builtin?