The id of the define block to use. To reference blocks inside an imported configuration, use the following syntax:
importedName::defineBlockName
Example
<!-- references a reference inside the current mapping -->
<useref refid="define1" />
<!-- references a define block from an external mapping which is imported in the
current mapping(imported1) -->
<useref refid="imported1::define1" />
<!-- here the current configuration imports imported1 which imports imported2. The
reference references define1 inside imported2 -->
<useref refid="imported1::imported2::define1" />