[xsl] offtopic: xs:schema - how to declare compulsory presence of either one (specific)string or group of nodes

["Mtekel" <thx@xxxxxxxxx>]

Hello,

I have one offtopic question about xs:schemas:
I want to validate xml document that contains some nodes, or information
that these are missing:

<my_doc>
  <table1>
    <item1>text</item1>
    <item2>text</item2>
        ........
   </table1>
   <table2>MISSING!</table2>
   <table3>
      <itemA>number</itemA>
      <itemB>date</itemB>
   </table3>
</my_doc>

That means, I have a list of tables, for each table also list of nodes it
should contain (with their value restrictions), but sometimes they are not
present and instead there is "MISSING!" string. Therefore - every table can
contain either "MISSING!" or specified group of nodes (depending on table
type - e.g. in the example table1, table2 and table3 are different and may
contain different sets of nodes)

How to specify this in xs:schema?

Thanks for any suggestions.

Michael