更多的正则表达式元字符

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Unusual occurrences happened at the fair.

Patty won fourth place in the 50 yard dash square and fair.

Occurences like this are rare.

The winning ticket is 55222.

The ticket I got is 54333 and Dee got 55544.

Guy fell down while running around  the south bend in his last event.

/\<fourth\>/

   需要在每一行中搜索的是所有包含单词fourth的行。\<表示的是锚定单词的开始.\>表示锚定单词的结束。被搜索的单词可以被空格分割，以标点符号结束，在一行的开始，或者在一行的未尾等等。