doc/syntax.tex: Mention superclass list is mandatory.

And discuss the difficulties of actually defining new root classes.

diff --git a/doc/syntax.tex b/doc/syntax.tex
index 15948cb..64b10f4 100644 (file)
--- a/doc/syntax.tex
+++ b/doc/syntax.tex
@@ -616,7 +616,10 @@ names, to distinguish them from other kinds of identifiers.
 
 The @<list>$[\mbox{@<identifier>}]$ names the direct superclasses for the new
 class.  It is an error if any of these @<identifier>s does not name a defined
-class.
+class.  The superclass list is required, and must not be empty; listing
+@|SodObject| as your class's superclass is a good choice if nothing else
+seems suitable.  It's not possible to define a \emph{root class} in the Sod
+language: you must use Lisp to do this, and it's quite involved.
 
 The @<properties> provide additional information.  The standard class
 properties are as follows.