evaluating it this way resets the variable using its initial value
expression even if the variable already has some other value.
\(Normally `defvar' and `defcustom' do not alter the value if there
-already is one.) In an analogous way, evaluating a `defface'
-overrides any customizations of the face, so that it becomes
-defined exactly as the `defface' expression says.
+already is one.)
If `eval-expression-debug-on-error' is non-nil, which is the default,
this command arranges for all errors to enter the debugger.