ruleFor method
Creates a new builder to represent a list of rules.
Implementation
AbstractRuleBuilder<E> ruleFor(dynamic Function(E e) func,
{required String key, bool useKeyAsElementName = false}) {
final AbstractRuleBuilder<E> builder = AbstractRuleBuilder<E>(
expression: func, key: key, useKeyAsElementName: useKeyAsElementName);
ruleBuilders.add(builder);
return builder;
}