This custom control will do all the validation instantly as the user enters the values into the field.  No waiting for the refresh or any outside influence.  This is client side and all as it as entered using dijit.form.ValidationTextBox, standard regEx formulas and your chosen error message.

This is a result of a numeric with single space separator only regEx formula( ^[-+]?[0-9]{1,}([\s;]?[-+]?[0-9]+){0,}$ ):
Invalid value:                   Error free value:   

The regEx formula may look complex and difficult to do.  Here is a great source for all your formula needs. 

I have found this to be the simplest, most reliable, and quickest validation there is.  It is easily adaptable to a standard text control also by just copying what you find in this control.  All the values are set using the custom controls Custom Properties are and fully customizable to your page.  These can be used within Repeat controls, and obviously multiple times on a single Xpage as needed.