src/main/java/com/github/fge/grappa/parsers/BaseParser.java
@DontLabel
    public Rule optional(final Object rule, final Object rule2,
        final Object... moreRules)
    {
        Objects.requireNonNull(moreRules);
        return optional(sequence(rule, rule2, moreRules));
    }
@DontLabel
    public Rule optional(final Object rule, final Object rule2,
        final Object... moreRules)
    {
        Objects.requireNonNull(moreRules);
        return optional(sequence(rule, rule2, moreRules));
    }
Try and match a given set of rules once

<p>This rule will therefore never fail.</p>

@param rule the first subrule
@param rule2 the second subrule
@param moreRules the other subrules
@return a rule