Yeah, I got that in the meantime.

Considering that the first version of your node Re^3: What is $::| ? read

"Like the OP said, it's not valid Perl. Are you asking me to speculate if $| and $main::| would be the same if $main::| was valid? Probably. It is the case for $_ "

it appears that it did take even you a second thought to figure out that one needs to write ${'main::|'}  :)