I've just sent Sean Burke a patch which allows you to use perldoc to search perlvar. I hijacked the -A switch because it was free and -V defaulted to 'version'. Didn't understand the option handling code, but I didn't try too hard. It's smart enough to know how to handle 'dollar digit' variables (e.g., regex matches), and if there's more than one name for a variable, it pulls the first one:
$ perldoc -A $^I
The current value of the inplace-edit extension. Use "undef" to disable
inplace editing. (Mnemonic: value of -i switch.)
Heck, I don't even know what an "inplace-edit extension" is, but this patch will at least tell you the variable.