$work =~ s{%(\w+)(?:\.(\w+))?}{
    defined $2
        ? $self->{'VARS'}{$1}{$2}
        : $self->{'VARS'}{default}{$1}
}eg;

##</code><code>##

my $fml = $self->{'VARS'};
$work =~ s{ % ( \w+ (?:\.\w+)* ) }{ dive($fml, split /\./, $1) }xegr;