+while (my ($browser, $row) = each %{ $caniuse->{agents} }) {
+ $versions{$browser} = [@{ $row->{versions} }];
+}
+
+my $ref = showlink('Can I use', 'https://caniuse.com/');
+$ref =~ s/(?=>)/ title="updated $_"/
+ for map { s/[\sT].*//r } $caniuse->{-date} || ();
+$ref = "Fyrd's $ref page";
+say '<p id="intro">Alternate rendition of '.$ref;
+
+my ($canihas, $usage);
+my $minusage = $get{threshold} // 1;
+given ($get{usage} // 'wm') {
+ when (!$_) {
+ # none
+ }
+ when (!m{ \A [a-z]\w+ (?:/\d[\d-]*\d)? \z }x) {
+ Alert([
+ 'Invalid browser usage data request',
+ 'Identifier must be alphanumeric name or <q>0</q>.',
+ ]);
+ }
+ $canihas = eval { Data("data/browser/usage-$_") } or do {
+ Alert('Browser usage data not found', $@);
+ break;
+ };
+ $usage = $_;
+ my $ref = $canihas->{-title} || 'unknown';
+ $ref = showlink($ref, $_)
+ for $canihas->{-site} || $canihas->{-source} || ();
+ $ref =~ s/(?=>)/ title="updated $_"/ for $canihas->{-date} || ();
+ print "\nwith $ref browser usage statistics";
+}
+
+my @browsers;
+if ($usage) { # first() does not work inside given >:(
+ # adapt version usage to actual support data
+ my %engineuse; # prefix => usage sum
+ for my $browser (keys %versions) {
+ my $row = $canihas->{$browser} // {};
+ my $verlist = $versions{$browser} or next;
+ if ($minusage and sum(values %$row) < $minusage) {
+ delete $versions{$browser};
+ next;
+ }
+ my %supported = map { $_ => 1 } @$verlist;
+
+ # cascade unknown versions
+ $row->{$_} //= undef for @$verlist; # ensure stable keys during iteration
+ while (my ($version, $usage) = each %$row) {
+ next if defined $supported{$version};
+ my $next = first { paddedver($_) ge paddedver($version) } @$verlist
+ or warn("No fallback found for $browser v$version; $usage% ignored"), next;
+ $row->{$next} += $usage;
+ $row->{$version} = 0; # balance browser total
+ }
+
+ # build row list for each version
+ if ($minusage) {
+ my @vershown; # $verlist replacement
+ my ($rowusage, @verrow) = (0); # replacement row tracking
+ for (@$verlist) {
+ push @verrow, $_; # queue each version
+ if (($rowusage += $row->{$_}) >= $minusage) {
+ push @vershown, [@verrow]; # add row
+ ($rowusage, @verrow) = (0); # reset row tracking
+ }
+ }
+ push @vershown, \@verrow if @verrow; # always add latest
+ @$verlist = @vershown;
+ }
+ else {
+ @$verlist = map { [$_] } @$verlist;
+ }
+
+ # reusable aggregates (grouped by prefix (engine) and browser)
+ $engineuse{ $caniuse->{agents}->{$browser}->{prefix} } +=
+ $row->{-total} = sum(values %$row);