^start of string
\s*any whitespace character, repeated any number of times
1-9one character from 1 (4910) to 9 (5710)
*matches any number of characters from the set below:
0-9one character from 0 (4810) to 9 (5710)
\s*any whitespace character, repeated any number of times
Positive Lookahead(?=([., \t])) .the literal . (4610 / 568 / 2E16)
,the literal , (4410 / 548 / 2C16)
the literal (3210 / 408 / 2016)
\ta tab character (ASCII 9)
Non-Capturing Group(?:\s*(?:\1|\r?\n)\s*[1-9][0-9]*)+ +repeats the group contents below at least once:
\s*any whitespace character, repeated any number of times
Non-Capturing Group(?:\1|\r?\n) \1the text saved by group 1
\r?optionally matches a carriage return (ASCII 13)
\na line-feed (newline) character (ASCII 10)
\s*any whitespace character, repeated any number of times
1-9one character from 1 (4910) to 9 (5710)
*matches any number of characters from the set below:
0-9one character from 0 (4810) to 9 (5710)
\s*any whitespace character, repeated any number of times
$end of string, or before its final line terminator