[。] 相当于逃避。（点）字符，即 \\。。

[.] is equivalent to escaping the . (dot) character, i.e. \\..

一旦角色出现在角色类中，它失去了作为特殊角色的地位。

Once the character appears in a character class, it loses its status as a special character.

由于 foo 不包含任何点，所以没有任何匹配。另一方面，。+ 是一个匹配所有内容的通配符贪婪表达式。

As foo doesn't contain any dots, nothing is matched. .+, on the other hand, is a wildcard greedy expression that matches everything.