it's really the underlying macro system that's recursive - http://www.w3.org/TR/html4/intro/sgmltut.html#h-3.3.2 http://www.w3.org/TR/html4/intro/sgmltut.html#h

it's really the underlying macro system that's recursive - http://www.w3.org/TR/html4/intro/sgmltut.html#h-3.3.2 http://www.w3.org/TR/html4/intro/sgmltut.html#h-3.3.2 and that's probably because macros systems typically are recursive since they are otherwise fairly limited, so this is a way to give them sufficient expressive power. so the explanation is probably "tradition" (and likely made more sense in sgml, which was the precursor to html).