Of course @_
could mean anything, but it means just one thing, which is documented in the perlvar man page:
@_ Within a subroutine the array @_
contains the parameters passed to that subroutine.
Access to the man pages does not make one an expert, anyone can read them. I seriously hope that anyone who is intending to successfully understand or modify code know enough about the language it is written in to actually be able to read it.
There are idioms in every language, especially in syntax. Python's inheritance declaration looks like a function call or an argument specification. Ruby's uses < to indicate inheritance. PHP and Perl are more self-documenting in this regard, using "class _subclass_ extends _baseclass_" and by assigning to a variable named ISA within a package respectively. Python's decorator syntax is non-obvious, and uses a perl-ish sigil to boot. Ruby using sigils to indicate scope (vs type, which is how it is done in both perl and older BASICs) is non-obvious. Python syntax for single element tuple creation. PHP's arrays allowing both integer and string indexing in the same array, and its "hashes" or "dicts" keeping order, leads to idiomatic code. Perl assignment list expanstion when using arrays and hashes as subelements on the LHS eating up the rest of the input is idiomatic. unless is idiomatic in perl, but only because few other languages have that kind of construct, and instead force you to use an if-not, which isn't always as readable. Perl's map and sort look like they can take closures, but they're really BLOCKs which is slightly different. The difference between Proc objects, blocks and lambdas and how they can be converted between each other and called in ruby is idiomatic.
Latin is readable if you speak Latin -- for everyone else it's pretty unreadable.