Regular Expressions 101

Explanation

Pro

Negative Lookahead(?!.*?(?:<h1>|<div>))

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

Non-Capturing Group(?:<h1>|<div>)

1st Alternative<h1>

<h1>the literal text <h1> (case sensitive)

2nd Alternative<div>

<div>the literal text <div> (case sensitive)

^start of line

Group 1(.+)

.+any character (except for line terminators), repeated at least once

$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.

25 tokens

(?!.*?(?:<h1>|<div>))^(.+)$

<h1>Headline</h1>
That should be paragraph 1.

That should be paragraph 2.

<div>Something.</div>
That should be paragraph 3.

<p>$1</p>

<h1>Headline</h1>
That should be paragraph 1.

That should be paragraph 2.

<div>Something.</div>
That should be paragraph 3.