what are the use of parentheses in this Lua pattern?
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base string is: `IP: 192.168.0.1`

Passing that string to string.gmatch function(besides below patterns) will return the following results:

pattern: `IP: (%d+.%d+.%d+.%d+)`
-->192.168.0.1

pattern: `IP: %d+.%d+.%d+.%d+`
-->IP: 192.168.0.1

My question is that what are the meaning of those parentheses to the Lua pattern matching engine?
Why by using the parentheses in the first pattern, the `IP: ` string omitted but in the second pattern no?