+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
a-z matches a single character in the range between a (index 97) and z (index 122) (case insensitive)
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case insensitive)
_ matches the character _ with index 9510 (5F16 or 1378) literally (case insensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case insensitive)
- matches the character - with index 4510 (2D16 or 558) literally (case insensitive)
This hyphen is treated literally, which might be confusing for others. Consider escaping it or placing at the start or end of the class!