Regular Expression is a text pattern that includes ordinary characters (for example, letters between a and z) and special characters (called "metacharacters").
Regular expressions use a single string to describe and match a series of strings that match a certain syntax rule.
Regular Expressions - Syntax syntax
Regular expression describes a string matching pattern (pattern), which can be used to check whether a string contains a certain substring, replace the matching substring, or extract a certain string from a string that matches a certain substring. Substrings of conditions, etc.
Regular Expressions - Syntax example
The following regular expression matches chapter titles with any number of digits:
/Chapter [1-9][0-9]*/