I do not know if validation is available.
I set up my zipcode search to be Contains (Default), Begins with, Exact.
If a user leaves it blank, with Contains, all records are included.
if a user provides 44, with Begins with, all from 44000 to 44999 are included.
If a user supplies 44221, with Exact, all with only 44221.
I hope you get a better answer for your validation question.
Dan