At I came across this use of the Question mark (use "password" as keyword and you&#039;ll find it quickly): <BR><BR>^(?=.*d)(?=.*[a-z])(?=.*[A-Z]).{4,8}$ <BR><BR>This doesn&#039;t seem to quite fit with any RegEx syntax I can find a reference to. I can see what this expression is meant to do, but why is that syntax acceptable? Maybe there is a *really definitive* treatment of syntax I haven&#039;t found yet?<BR>