Regular Expressions 101

Pro

Negative Lookbehind(?<!^(?:(?:\d+|[A-Z])\.?)?)

^start of line

Non-Capturing Group(?:(?:\d+|[A-Z])\.?)?

?repeats the group contents below at most once:

Non-Capturing Group(?:\d+|[A-Z])

1st Alternative\d+

\d+a digit, repeated at least once

2nd Alternative[A-Z]

Character Class[A-Z]

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

\.?optionally matches the literal . (46₁₀ / 56₈ / 2E₁₆)

\ta tab character (ASCII 9)

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.

26 tokens

Regular Expression

(?<!^(?:(?:\d+|[A-Z])\.?)?)\t

New

	text
1.	text
1	text
A.	text
text	text

That is, it shouldn't match tabs that are
 at the beginning of the text,
 after a listed item mark [A-Z] or [0-9]. Here is my expression:

Substitution

	text
1.	text
1	text
A.	text
text	text

That is, it shouldn't match tabs that are
 at the beginning of the text,
 after a listed item mark [A-Z] or [0-9]. Here is my expression: