\ba Unicode word boundary
Character Class[0-9]{1,2} {1,2}matches between 1 and 2 characters from the set below:
0-9one character from 0 (4810) to 9 (5710)
\s+a Unicode whitespace character, repeated at least once
\S+any character that is not Unicode whitespace, repeated at least once
\s+a Unicode whitespace character, repeated at least once
{4}matches exactly 4 characters from the set below:
0-9one character from 0 (4810) to 9 (5710)
\ba Unicode word boundary
g modifier: global. Finds all matches instead of stopping after the first