The System'To_Address
(System is the only permissible prefix)
denotes a function identical to
System.Storage_Elements.To_Address except that
it is a static attribute. This means that if its argument is
a static expression, then the result of the attribute is a
static expression. The result is that such an expression can be
used in contexts (e.g. preelaborable packages) which require a
static expression and where the function call could not be used
(since the function call is always non-static, even if its
argument is static).