/usr/share/doc/libxml-sax-machines-perl/examples/output_to_process is in libxml-sax-machines-perl 0.46-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | use XML::SAX::Machines qw( Pipeline );
Pipeline(
"<$ARGV[0]",
## Put some filter here :)
"| xmllint --format -"
)->parse;
|