I have always answered this kind of question with what ever translates as 'in the upper third of your range'. We can explore things from there if they are interested.

There is a lot about Perl (and many other things) that I don't know. I know that. I also know where to go to (re)read about it. I am striving to be honest about the breath of my knowledge in the face of a simplistic rating scheme.

There are very few things where I know that I know everything there is to know about the subject. And, there are some subjects where I know that I have read everything currently available. Most everything else falls in to the 'I know enough to follow your argument, and if you want more detail, here is where I was reading about it a while back' category...

I figure that I loose out on some gigs because of this attitude. On the other hand, a number of folks have come back when the contract comes in six weeks early and said: "you under-rated your self on the questionnaire; we are adding a performance bonus for finishing early." And I get a lot of repeat customers this way.

Life is too short (especially at my age) to remember all of the detailed nits about pack()/unpack(); knowing that there is a table in the Perl In A Nutshell, however....