http://www.w3.org/hypertext/WWW/MarkUp/html-spec/html-spec_4.html#SEC37
Thu Jun 8 15:08:56 1995
Example and Listing: XMP, LISTING
The XMP and LISTING elements are similar to the PRE element, but they
have a different syntax. Their content is declared as CDATA, which
means that no markup except the end-tag open delimiter-in-context is
recognized (see 9.6 "Delimiter Recognition" of [SGML]). (18)
Since CDATA declared content has a number of unfortunate interactions
with processing techniques and tends to be used and implemented
inconsistently, HTML documents should not contain XMP nor LISTING
elements -- the PRE tag is more expressive and more consistently
supported.
The LISTING element should be rendered so that at least 132 characters
fit on a line. The XMP element should be rendered so that at least 80
characters fit on a line but is otherwise identical to the LISTING
element. (19)