Several rules of the regular expression engine

The rule 1:regex engine matches the input string as soon as it starts. It searches for one character at a time until a match is found

Rule 2: After a matching start is found, the Regex engine will continue to match until it encounters a character that is not received by the pattern

The rule 3:regex engine is very greedy--as long as the pattern allows, it will match as many characters as possible

The rule 4:regex engine is eager to implement a match, so it will backtrack as needed to achieve a match

The rule 5:regex engine always chooses the first option

　　

Several rules of the regular expression engine