/// <summary>
/// The rule that indicates <see cref="Nonterminal"/> does not appear in the input text.
/// </summary>
/// <param name="lhs">The <see cref="OptionalNonterminal{T}"/> represeting the LHS of the rule.</param>
public static void Rule(OptionalNonterminal <T> lhs)
{
}
/// <summary>
/// The rule that indicates the <see cref="Nonterminal"/> appears in the input text.
/// </summary>
/// <param name="lhs">The <see cref="OptionalNonterminal{T}"/> represeting the LHS of the rule.</param>
/// <param name="rhs">The <see cref="Nonterminal"/> representing the RHS of the rule.</param>
public static void Rule(OptionalNonterminal <T> lhs, T rhs)
{
lhs.Rhs = rhs;
}