title: Validate enumeration based on date ranges in XSD 1.0?
body: <p>In XSD I would like to define a type <code>Country</code> including a restriction which sets the list of country names that can be used.
  Which can be done easily by using enumeration as a restriction.</p>
  <p>However, this list will vary when time goes by. For example: in the past we had Yugoslavia which doesn't exist anymore; Croatia, Slovenia, etc appeared instead.
  So a country will have a start date and (potentially) an end date. <code>StartDate</code> and <code>EndDate</code> will set the date range of  existence for each particular country.</p>
  <p>When validating an XML I would like to verify whether the XML refers to an existing country.
  Therefore the XML will also contain variable <code>ReferenceDate</code> which will be used to check against StartDate and EndDate.</p>
  <p>Actually I would like to define type <code>Country</code> with attributes <code>CountryName</code>, <code>StartDate</code> and <code>Enddate</code> set.
  When validating the XML with - for example - values Croatia and <code>ReferenceDate</code> I would like to verify whether Croatia is a valid country at date <code>ReferenceDate</code>, using type <code>Country</code> being defined in the XSD.</p>
  <p>Any ideas with the restriction given that I'm using XSD 1.0?</p>