\newenvironment

 \newenvironment{nam}[args]{begdef}{enddef}
 \renewenvironment{nam}[args]{begdef}{enddef}

These commands define or redefine an environment.

nam

The name of the environment. For \newenvironment there must be no currently defined environment by that name, and the command \nam must be undefined. For \renewenvironment the environment must already be defined.

args

An integer from 1 to 9 denoting the number of arguments of the newly-defined environment. The default is no arguments.

begdef

The text substituted for every occurrence of \begin{nam}; a parameter of the form #n in cmd is replaced by the text of the nth argument when this substitution takes place.

enddef

The text substituted for every occurrence of \end{nam}. It may not contain any argument parameters.