Property Constraint dependent on another property

[wireframe]

How can I implement a constraint that is dependent on the input of another property? I've searched through the sample apps and haven't found anything. Here's what i'm trying:

add("hitpoints", new Constraint() {
  public boolean test(Object object) {
    Integer value = (Integer) object;
    //need to lookup another property to determine if this is a valid input.
  }
}

[aktp]

you need to use 'PropertiesConstraint'

[wireframe]

the PropertiesConstraint works great. Thanks!