Look around and find out

Sometimes we want to see if something is followed by something else without actually including the second part.
That’s where lookaheads and lookbehinds come in.

(?=) - Positive lookahead
(?!)- Negative lookahead
(?<=) - Positive lookbehind
(?<!) - Negative lookbehind

What you’re looking for goes inside the parentheses.

For example:
\w+(?=\.pdf) - matches any word followed by .pdf (excluding the .pdf)

Sadly, not all browsers support lookbehinds, so we will focus on lookaheads for now