Install flexml by entering the following commands in the terminal:
sudo apt update sudo apt install flexml
Description:
Fast validating XML processors and applications generator
FleXML makes it easy to generate very fast validating XML processors as flex(1) source. . By design it can only handle documents using an external DTD.
Homepage: http://flexml.sourceforge.net/
Version: 1.9.6-5
Section: universe/devel