为什么看起来regexp＆＃39; OR对订单敏感吗？

Question

print(nltk.regexp_tokenize('That U.S.A. poster-print costs $12.40...13.10', r"((?:(?:[A-Z]\.)+)|(?:\w+(?:-\w+)*)|(?:\d+(?:\.\d+)?))"))

输出：

"['That', 'U.S.A.', 'poster-print', 'costs', '12', '40', '13', '10']"

并且（按括号中的模式顺序改变）：

print(nltk.regexp_tokenize('That U.S.A. poster-print costs $12.40...13.10', r"((?:(?:[A-Z]\.)+)|(?:\d+(?:\.\d+)?)|(?:\w+(?:-\w+)*))"))

输出：

['That', 'U.S.A.', 'poster-print', 'costs', '12.40', '13.10']

为什么这种情况下的订单很重要？