tnc(3tcl) on Linux
The text afa074da5b47, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster) shipped it. The page shows this text now.
tnc is an expat parser object extension, that validates the XML stream against the document DTD while parsing.