$tree -> parse_file ($file); # $tree is a XML::TreeBuilder
my @results = $tree -> look_down ('attr' => 'value');

##</code><code>##

timethis (5000, sub {$tree -> parse_file ($file)});
timethis 5000: 16 wallclock secs (12.98 usr +  1.41 sys = 14.39 CPU) @ 347.46/s (n=5000)

##</code><code>##

timethis (5000, sub {my @results = $tree -> look_down('attr' => 'value')});
timethis 5000:  2 wallclock secs ( 1.42 usr +  0.00 sys =  1.42 CPU) @ 3516.17/s (n=5000)

##</code><code>##

timethis (500, sub {$tree -> parse_file ($file); my @results = $tree -> look_down('attr'=> 'value')});
timethis 500: 36 wallclock secs (34.32 usr +  0.19 sys = 34.51 CPU) @ 14.49/s (n=500)