A mask is a regular expression that represents text that should be ignored during a comparison.
一个蒙版就是个正则表达式，它代表了一次比较期间应该被忽略的文本。
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It says that the function must be used in an expression involving the comparison operation and that the search method "equals" of the index extension hash_index is referred to.
To use a regular expression in Squirrel Shell, you define the regular expression, compile it, make a comparison, then iterate over the results, if any.