The various query types are represented as subclasses:
To create a new query, you call the constructor of the corresponding class.
To modify or retrieve the content of a query, call the corresponding mutator:
my $query = GStreamer::Query::Position -> new("time");
$query -> position("time", 23);
my ($format, $position) = $query -> position;
my $query = GStreamer::Query::Duration -> new("time");
$query -> duration("time", 23);
my ($format, $duration) = $query -> duration;
