.
.*
.?
.+
..
...
tianguo?
tianguo+
tianguo*
tianguo
^tianguo
tianguo$
[tianguo]
[^tianguo]
(tianguo)?
(tianguo)+
(tianguo)*
(tianguo){1,10}
(tianguo){,10}
(tianguo){10,}
tianguo (?=pretty)
tianguo (?!=urgly)
(?<=young) tianguo
(?<!old) tianguo
\btianguo\b
(tianguo)+?
（tianguo)\1{99}
