A proper choice of macro definitions can encode semantic information about the
visual layout being used. For instance, an author wishing to use the notation
[tex2html_wrap331] to denote the Legendre symbol could define a new command
\legendre that produces the desired layout. In the absence of this
facility, e.g.,when using an SGML Math DTD that does not know about Legendre
symbols, the author would be restricted to encoding [tex2html_wrap333] in terms
of the basic operators provided, in this case, the operator that stacks its
arguments. Though both encodings would produce the desired visual layout on
paper, the encoding using the \legendre macro has the advantage that an
application can interpret the use of the notation as meaning a Legendre
symbol.