Not to mention that the original almost 21 year old perl1 manpage version contains no such disclaimers about it being pseudo code.

The null filehandle <> is special and can be used to emulate the behav
+-
ior of sed and awk.  Input from <> comes either from standard input, o
+r
from  each  file  listed on the command line.  Here's how it works: th
+e
first time <> is evaluated, the ARGV array is checked,  and  if  it  i
+s
null,  $ARGV[0]  is  set  to  '-', which when opened gives you standar
+d
input.  The ARGV array is then processed as a list of  filenames.   Th
+e
loop

     while (<>) {
          ...            # code for each line
     }

is equivalent to

     unshift(@ARGV, '-') if $#ARGV < $[;
     while ($ARGV = shift) {
          open(ARGV, $ARGV);
          while (<ARGV>) {
               ...       # code for each line
          }
     }

except  that it isn't as cumbersome to say.  It really does shift arra
+y
ARGV and put the current filename into variable  ARGV.   It  also  use
+s
filehandle  ARGV  internally.  You can modify @ARGV before the first <
+>
as long as you leave the first filename at the beginning of the  array
+.
[download]

Not to mention that presuming as tye does above that that there was to be an implied < prepended to filenames doesn't make any sense because that would break the very explicitly documented behavior of an argument of '-' triggering the 'magic two-arg open of "-" opens STDIN' behavior (which, again, was explicitly meant to behave this way and has done so for 20+ years worth of perls.)