Validation patterns can be added to form fields like phone number or email address so that it accepts the number or email if it matches the set pattern. 

Here are some sample pattern:

Phone: <input type="text" name="Phone Number" pattern="[7-9]{1}[0-9]{9}"

This would only accept 10 digits and the first number should start with 7,8 or 9 and then the remaining 9 numbers could be anything between 0 and 9. This is a format which works for Indian numbers.

Sample Email Validation pattern: 

function validateEmail(elementValue){      
   var emailPattern = /^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}$/;
   return emailPattern.test(elementValue);

This would only accept an email address that starts with any uppercase or lower case alphabets and numbers and has @ and then allows alphabets and numbers and 2 to 4 characters after the period (.). This is to separate domain and subdomain names.
validation pattern