Regex: what does (?! …) mean?

Question

The following regex finds text between substrings FTW and ODP.

/FTW(((?!FTW|ODP).)+)ODP+/

What does the (?!...) do?

Answer 1

Regex

/FTW(((?!FTW|ODP).)+)ODP+/

matches first FTW immediately followed neither by FTW nor by ODP, then all following chars up to the first ODP (but if there is FTW somewhere in them there will be no match) then all the letters P that follow.

So in the string:

FTWFTWODPFTWjjFTWjjODPPPPjjODPPPjjj

it will match the bold part

FTWFTWODPFTWjjFTWjjODPPPPjjODPPPjjj