Regular expression and Extend regular expression

Basic (BRE) and extended (ERE) regular expression

When using Regular expression, it's confusing that "(" have different meaning in different tools.

For example, it will match the "(" text in GVIM's regular expression, but may means Character group in other situation.

The root cause is that we have Basic regular expression and extended regular expression.

See detail in following page:

https://www.gnu.org/software/sed/manual/html_node/BRE-vs-ERE.html#BRE-vs-ERE