I want to validate this using XML Schema. So I trying to create a simpleType derived from xsd:String but I'm having some problems. Can anyone help? What is wrong with this simpleType? Why can't it meet my requirements stated above?
And similarly for other elements you wish to join with "or". The only time you should use braces  or "or" something is when you're talking about single characters. E.g.  means 1 or 2 or 3, fine. But the whole expression is just one character (which can be one of thee possibilities. If you want to "or" things that are longer than one character, you need | instead.