# takes care of [tag://target|alt]
$chunk =~ s/\[(\w+):\/\/(.*?)\|([^\]]+)\]/<a href="$TAG{$1}$2">$3<\/a>/g;

# takes care of [tag://target]
$chunk =~ s/\[(\w+):\/\/([^\]]+)\]/<a href="$TAG{$1}$2">$2<\/a>/g;

# takes care of [target]
$chunk =~ s/\[([^\]]+)\]/<a href="$TAG{DEFAULT}$1">$1<\/a>/g;