Then, you can do it with behaviors in DW. With your 'input' for number field selected either in code or design view, go to 'Behaviors' panel (if it is now shown already, click Window > Behaviors to show it).
Click the 'Plus' callout button > Validate Form.
Choose the field that you're validating (in your case, id_number). Accept 'Number from' 10 to 10 (min and max 10). Hit OK.
Btw, just so you know, Spry is no longer being officially supported by Adobe. http://blogs.adobe.com/dreamweaver/2012/08/update-on-adobe-spry-framework-availability.htm l
Start moving to/ learning jQuery.