{disallowed substitutions} with a simple type definition?

3.3.4 Element Declaration Validation Rules

4.3 The ·local type definition· must be validly derived from the {type
definition} given the union
                of the {disallowed substitutions} and the {type
definition}'s {prohibited substitutions}, as
                defined in Type Derivation OK (Complex) (§3.4.6) (if it
is a complex type definition), or given
                {disallowed substitutions} as defined in Type Derivation
OK (Simple) (§3.14.6) (if it is a
                ^^^^^^^^^^^^^^^^^^^^^
                simple type definition).

Does anyone know what this "{disallowed substitutions}as defined in Type
Derivation
OK (Simple)" is?

I know about the {disallowed substituitions} with an element declaration
and
{prohibited substitutions} with a complex type definition.  But, what is
the
{disallowed substituitions} associated with a simple type defintion?

Thx,

-Stanley