The element type dcc:validXMLList is used to specify foot notes for si:realListXMLList elements in a DCC. You can specify a list of boolean valuesa separated by a space to specify where the data from the meta data belongs to (see the XML example below).
<xs:element name="validXMLList" type="dcc:booleanXMLListType"/>
If you would want to display following table with the following foot note.

You have to have the following structure in your DCC with version greater or equal to 3.2.0.
<dcc:quantity refType="basic_xxx">
<dcc:name>
<dcc:content lang="en">Transmission coefficient phase shift</dcc:content>
</dcc:name>
<si:realListXMLList>
<si:valueXMLList>-0.02 -0.03 -0.02 -0.02 -0.01</si:valueXMLList>
<si:unitXMLList>\degree</si:unitXMLList>
</si:realListXMLList>
<dcc:measurementMetaData>
<dcc:metaData>
<dcc:declaration>
<dcc:content lang="en">This comment is only valid for the third element of the realListXMLList.</dcc:content>
</dcc:declaration>
<dcc:validXMLList>false false true false false</dcc:validXMLList>
</dcc:metaData>
</dcc:measurementMetaData>
</dcc:quantity>