.. in scalar context is a flipflop operator that does what you describe like this:

while (<DATA>) {
   # skip everything from line 1 to the #cardtype line
   unless (1../^#cardtype$/) {
      # we're past the junk
   }
}
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It works by returning true once the first condition is met (where the constant 1 here is implicitly compared to the current input line number) and continues to return true until the second condition is met. See perldoc perlop for more information.