@vindex t
@kindex setting-constant
- XEmacs Lisp has two special symbols, @code{nil} and @code{t}, that
-always evaluate to themselves. These symbols cannot be rebound, nor can
-their value cells be changed. An attempt to change the value of
-@code{nil} or @code{t} signals a @code{setting-constant} error.
+In XEmacs Lisp, some symbols always evaluate to themselves: the two
+special symbols @code{nil} and @code{t}, as well as @dfn{keyword
+symbols}, that is, symbols whose name begins with the character
+@samp{@code{:}}. These symbols cannot be rebound, nor can their value
+cells be changed. An attempt to change the value of @code{nil} or
+@code{t} signals a @code{setting-constant} error.
@example
@group
If the first character of @var{doc-string} is @samp{*}, it means that
this variable is considered a user option. This lets users set the
-variable conventiently using the commands @code{set-variable} and
+variable conveniently using the commands @code{set-variable} and
@code{edit-options}.
For example, this form defines @code{foo} but does not set its value: