Regular Expressions 101

Pro

(?ms)applies the following effective flags to the remainder of the pattern: gms

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

s modifier: single line. Allows a dot to match line terminators

^start of line

##the literal text ##

Negative Lookahead(?!#)

#the literal # (35₁₀ / 43₈ / 23₁₆)

.*?any Unicode character, repeated any number of times

Positive Lookahead(?=\n##(?!#)|\Z)

1st Alternative\n##(?!#)

\na line-feed (newline) character (ASCII 10)

##the literal text ##

Negative Lookahead(?!#)

#the literal # (35₁₀ / 43₈ / 23₁₆)

2nd Alternative\Z

\Zend of string

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

Detailed match information will be displayed here automatically.

25 tokens

Regular Expression

(?ms)^##(?!#).*?(?=\n##(?!#)|\Z)

New

## chapter 1

Lorem ipsum dolor sit amet, consectetur adipiscing elit. 
Suspendisse mollis magna nec felis gravida, id posuere libero molestie.

### subchapter 1.1

Sed vel ipsum eget tortor maximus ultrices vitae eget dolor.

## chapter 2

Aenean pellentesque lectus quis ex tristique ultrices. Vestibulum eget purus eu ipsum vestibulum pulvinar