<\body> The main key-combinations that you should know to write style files are the following: <\description> >creates a new assignment. The first argument is a new command name and the second argument an expression. >permits to locally change one or more environment variables. With statements are of the form x\|a\|\\|x\|a\|b\>, where the > are the names of the variables, the > their local values, and the text on which the local environment applies. >creates a macro. Arguments to the macro can be inserted using the -key. >get the value of a macro argument. >get the value of an environment variable. >expands the macro with zero or more arguments. More precisely, when evaluating a macro expansion \|\\|x}> created by , the following action is undertaken: <\itemize> If is not a string nor a macro, then is evaluated once. This results either in a macro name or a macro expression . If we obtain a macro name, then we replace by the value of the environment variable . If, after this, is still not a macro expression, then we return . Let ,\,y> be the arguments of and it's body (superfluous arguments are discarded; missing arguments take the empty string as their default value). Then we substitute > for each > in and return the evaluated result. <\initial> <\collection>