A variation on the assert&#39; macro in which the restart handler is bound<br> during the execution of the test-form, so that uses of this macro can be nested.<br> As with assert,' a setf-able place' may be given, but unlike assert,' only
one may be given. As with assert,&#39; you can give an error message, but you can<br> also give a message to go in the restart handler. That report message may also<br> use the arguments. It will usually say something like supply a new value for<br> foo.&#39;&#39; The restart is named continue,' and takes one argument, the value to
setf place' to. Like assert,' NIL is returned if test-form is true.