Regular Expression - + - matches one or more of the previous single expression

The plus sign (+) matches with one or more repetitions of the previous single expression.
a+ means the same as aa*
Using round brackets can put several expressions together to be repeated. e.g. (abc)+

Examples

Match line starting with 12 followed by one or more 3's:

^123+
This would match the following:
123
1233
12333333333333333
It would not match the following:
12 - no three
113 - 1 cannot be repeated at beginning
1123 - 1 cannot be repeated at beginning
1243 - 4 cannot be appear before 3

Match 123 repeated any number of times:

(123)+
This would match the following:
123
123123
123123123

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