class Regexp::Expression::Alternation

the API when it comes to handling the alternatives.
This is not a subexpression really, but considering it one simplifies

def <<(exp) 

def <<(exp)
  expressions.last << exp
end

def alternative(exp = nil) 

def alternative(exp = nil)
  expressions << (exp ? exp : Alternative.new(level, set_level, conditional_level))
end

def quantify(token, text, min = nil, max = nil, mode = :greedy) 

def quantify(token, text, min = nil, max = nil, mode = :greedy)
  alternatives.last.last.quantify(token, text, min, max, mode)
end

def starts_at 

def starts_at
  expressions.first.starts_at
end

def to_s(format = :full) 

def to_s(format = :full)
  alternatives.map{|e| e.to_s(format)}.join('|')
end