Guide to LaTeX (4th Edition) (Tools and Techniques

196 Chapter 8. User Customizations
\newenvironment{env name}[narg][opt]{beg def }{end def }
\renewenvironment{env name}[narg][opt]{beg def }{end def }
where the arguments have the following meanings:
env name: the name of the environment; for \newenvironment, it may
not be the same as any existing environment or command name,
whether L AT E X or user-defined. For \renewenvironment, on the other
hand, there must already be an environment bearing this name. Any
changes to L AT E X environments should only be undertaken if the user
knows what he or she is doing.
narg: a number between 1 and 9 that states how many arguments the
environment is to have; if the optional argument narg is omitted,
the environment is to have no arguments.
opt: the default text for the first argument (#1) if it is to be optional; this
behaves the same as for \(re)newcommand (page 185).
beg def: the initial text to be inserted when \begin{env name} is called;
if this text contains entries of the form #n, with n = 1, . . .,narg, then
when the environment is started with the call
\begin{env name}{arg 1}...{arg n}...
each occurrence of #n within beg def is replaced by the text of the
argument arg n.
end def: the final text that is inserted when \end{env name} is called;
here the dummy arguments #n are not allowed since they are only
to appear in the beg def text.
8.4.1 Environments without arguments
Just as for user-defined commands, environments without the optional
argument narg will be illustrated first. A user-defined environment named
sitquote is created with
\newenvironment{sitquote}{\begin{quote}\small
\itshape}{\end{quote}}
which sets the text appearing between \begin{sitquote} text \end
{sitquote} in the typeface \small\itshape, and indented on both
sides from the main margins, as demonstrated here.
In this case, beg def consists of the command sequence \begin{quote}
\small\itshape while end def is simply \end{quote}. Now the call
\begin{sitquote} text \end{sitquote} is the same as
\begin{quote}\small\itshape text \end{quote}