xsd - How can I extend restrictions on simple type element? -

Can anyone post an example about adding enumerated restrictions on the simple type element in the XML schema?

  & lt; Xs: simple type name = "myElement" & gt; & Lt; Xs: union member type = "previous revision" & gt; & Lt; XS: simpleType & gt; & Lt; Xs: restriction base = "xs: string" & gt; & Lt; Xs: calculation value = "closed" /> & Lt; / XS: Ban & gt; & Lt; / XS: simpleType & gt; & Lt; / XS: Union & gt; & Lt; / XS: simpleType & gt;