How to Implement dependency property on Textbox that allows numeric or alphanumeric values

I am using a textbox开发者_JAVA技巧 in a WPFApplication and I want to implement a dependency property that will decide whether textbox allow input as numeric or alphanumeric.

there are at least three ways to do this.
1) derive a sub-class, adding your dependency property
2) create an attached property
3) create and attach a behavior (using the expression SDK)