<sch:rule context="@class">
<sch:assert test="every $i in tokenize(., '\s+') satisfies substring($i,2)=//mei:category/@xml:id or
matches($i, '^([a-z]+://|\.{1,2}/)')">The value in @class must either correspond to the @xml:id attribute of a category
element or be an external URL.</sch:assert>
</sch:rule>
<classSpec ident="att.classed" module="MEI.shared" type="atts">
<desc>Attributes which can be used to classify features.</desc>
<attList org="group">
<attDef ident="class" usage="opt">
<desc>Contains one or more URIs which denote classification terms that apply to the entity
bearing this attribute.</desc>
<constraintSpec ident="check_classURI" scheme="isoschematron">
<constraint>
<sch:rule context="@class">
<sch:assert test="every $i in tokenize(., '\s+') satisfies substring($i,2)=//mei:category/@xml:id or
matches($i, '^([a-z]+://|\.{1,2}/)')">The value in @class must either correspond to the @xml:id attribute of a category
element or be an external URL.</sch:assert>
</sch:rule>
</constraint>
</constraintSpec>
</attDef>
</attList>
</classSpec>