^start of string
{4}matches exactly 4 characters from the set below:
0-9one character from 0 (4810) to 9 (5710)
-the literal - (4510 / 558 / 2D16)
{3}matches exactly 3 characters from the set below:
0-9one character from 0 (4810) to 9 (5710)
\ban ASCII word boundary
.+any character (except for line terminators), repeated at least once
$end of string, or before its final line terminator