Regular Expressions 101

^start of line

Non-Capturing Group(?:remind me )

remind me the literal text remind me (case sensitive)

.*?any character (except for line terminators), repeated any number of times

the literal (32₁₀ / 40₈ / 20₁₆)

Group 1(to|that|about|its|it's)?

?repeats the group contents below at most once:

1st Alternativeto

tothe literal text to (case sensitive)

2nd Alternativethat

thatthe literal text that (case sensitive)

3rd Alternativeabout

aboutthe literal text about (case sensitive)

4th Alternativeits

itsthe literal text its (case sensitive)

5th Alternativeit's

it'sthe literal text it's (case sensitive)

?optionally matches the literal (32₁₀ / 40₈ / 20₁₆)

Group 2(.*)

.*any character (except for line terminators), 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.

Search reference

Regular Expression

^(?:remind me ).*? (to|that|about|its|it's)? ?(.*)$

New

remind me in 24 hours test
remind me in 24 hours to test
remind me to test

E.g. These strings would work with your current pattern
two spaces after 'remind me' where the group fits in:
^(?:remind me ).*? (to....
             ^    ^
remind me  to test
remind me blabla to test

one or three or more, no:
remind me to test
remind me   to test
remind me bla bla to test

Regular Expression

Substitution