only a figure should be allowed with inserted snippet, not a table

[michaeldsmith]

According to @palemieux, this should produce an error but it does not currently produce an error, only a figure should be allowed with inserted snippet, not a table.

<table id="tab-xml-schema-root-element-definition">
   <caption>XML Schema root element definition</caption>
   <pre data-include="snippets/table-2.xml"></pre>
</table>

It renders like this