A WPF Text Control with Chilean RUT Mask

Given that RUT format responds to pattern NN.NNN.NNN-C, and I wished to prevent the user from putting any value that didn't correspond; I decided to create my first custom control from a TextBox to accept only the allowed values, besides giving the RUT mask automatically. This post shows how to create the control, define properties, handle behavior of the control, and finally tell us how to use the code.