... your map qr{...} join ... irritated me a bit, because the processed list has only one element.

Yeah, that gets to me a bit too, whenever I use it. But that syntax is used in haukex's original article, so I'm willing to consider it an "idiom." :)

The important point is that the regex elements be somehow converted into a regex object. It's at this stage that any necessary boundary assertions are added. The only reasonable alternative I can see is something like

my $rx_search =
    join ' | ',
    map  quotemeta,
    reverse sort
    keys %replace
    ;
$rx_search = qr{ ... $rx_search ... }xms;
[download]

> $rx_search = qr{ ... $rx_search ... }xms;

Ok it's somehow "wasting" a variable, but

my $rx_search = qr{$joined_search}xms;

wouldn't really irritate me.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}