Custom module to validate fields I am trying to create a custom module using webforms drupal 7 to carry out some form of validation. All i want the module to do to check if a value of one field (A) is entered then the other field (B) should be zero and if the value of field (B) is entered then the value of field (A) is zero. Anybody able to help? I am a newbee to drupal.
Webform Validation to the rescue!


  This module adds an extra tab to each webform node, allowing you to
  specify validation rules for your webform components. You can create
  one or more of the predefined validation rules, and select which
  webform component(s) should be validated against those.