Allow to use `if` condition with relations

[ixxvivxxi]

The documentation says that you can use if together with relations validations. Can anyone help me figure out how to use this?

[ixxvivxxi]

example:

validations = {
   types: {
      relations: {
        if(key, value, model) {
          return model.get('status') !== 'OK';
        },
        value: ['hasMany'],
      },
    },
    category {
      relations: {
        if(key, value, model) {
          return model.get('status') !== 'OK';
        },
        value: ['belongsTo'],
      },
    },
}