Regular Expressions 101

Explanation
Pro

^start of line

\s*a Unicode whitespace character, repeated any number of times

Group 1(\d{4}\b\s*)+

+repeats the group contents below at least once:

\d{4}a Unicode decimal digit, repeated exactly 4 times

\ba Unicode word boundary

\s*a Unicode whitespace character, repeated any number of times

$end of line

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Detailed match information will be displayed here automatically.

25 tokens

^\s*(\d{4}\b\s*)+$

New

1234 2345 2345 6754
1234 2312
1234 asdf 1232 2345 
2345 4567 2345
1234 231 2345