BUILT-IN COMMANDS
   The Tcl library provides the following built-in commands,
   which will be available in any application using Tcl.  In
   addition to these built-in commands, there may be additional
   commands defined by each application, plus commands defined
   as Tcl procedures.  In the command syntax descriptions
   below, optional arguments are indicated by enclosing their
   names in brackets;  apologies in advance for the confusion
   between this descriptive use of brackets and the use of
   brackets to invoke command substitution.  Words in boldface
   are literals that you type verbatim to Tcl.  Words in
   italics are meta-symbols;  they act as names to refer to a
   class of values that you can type.