These tools are used to convert XML and HTML to and from a line-oriented
format more amenable to processing by classic Unix pipeline processing
tools, like grep, sed, awk, cut, shell scripts, and so forth.  There are
four tools, xml2, 2xml, html2, and 2html.  None of them take any command-
line arguments; they are all simple filters, reading information from
standard input in one format and writing the same information to standard
output in a different format.