+
+ # Handle nested #if/#else.
+ if ($remainder =~ /^#\s*(?:ifndef|ifdef|if)\s/) {
+ push(@stack, [ $type, $level ]);
+ } elsif ($remainder =~ /^#\s*(?:else|elif)\b/) {
+ ($type, $level) = @{$stack[$#stack - 1]};
+ } elsif ($remainder =~ /^#\s*endif\b/) {
+ ($type, $level) = @{pop(@stack)};
+ }
+