^(?:[\t ]*(?:\r?\n|\r)){1,}

^ asserts position at start of a line
Non-capturing group (?:[\t ]*(?:\r?\n|\r)){1,}
{1,} matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
Match a single character present in the list below [\t ]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\t matches a tab character (ASCII 9)
matches the character with index 3210 (2016 or 408) literally (case sensitive)
Non-capturing group (?:\r?\n|\r)
1st Alternative \r?\n
\r matches a carriage return (ASCII 13)
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\n matches a line-feed (newline) character (ASCII 10)
2nd Alternative \r
\r matches a carriage return (ASCII 13)