mention built-in constants.

Doc/lib/libobjs.tex

-\chapter{Built-in Functions, Types, and Exceptions \label{builtin}}
+\chapter{Built-In Objects \label{builtin}}
 
-Names for built-in exceptions and functions are found in a separate
+Names for built-in exceptions and functions and a number of constants are
+found in a separate 
 symbol table.  This table is searched last when the interpreter looks
 up the meaning of a name, so local and global
 user-defined names can override built-in names.  Built-in types are
@@ -11,6 +12,7 @@ described together here for easy reference.\footnote{
 \indexii{built-in}{types}
 \indexii{built-in}{exceptions}
 \indexii{built-in}{functions}
+\indexii{built-in}{constants}
 \index{symbol table}
 
 The tables in this chapter document the priorities of operators by