validation.js

var obj = {
  name: 'Good McGoodson',
  last_menstrual_period: 41
};

validate(obj, [ "name.length between 1 and 100", "lmp between 0 and 40"]]); // returns ["lmp must be between 0 and 40"]

Expression parsing vs.

{
    field: 'name',
    validations: [
        {
            minLength: 2,
            maxLength: 100
        }
    ]
}

validationMessage would be automatically created based on the rule, but could be overwritten?