The variant-specific
<sw-compu-method>s are referenced in variant-specific
<sw-param>s and
<sw-variable>s. These must in turn differ in the
<short-name> as well as in the
<long-name> and can again be referenced in
<sw-function-variant>s. Thus variant handling is not carried out concealed (i.e. by processing in the DTD), but rather is exclusively defined by the user.