an>.attribute<br>
&nbsp;&nbsp;&nbsp;&nbsp;<span class="keywordsign">|</span>&nbsp;<span class="constructor">Pcf_extension</span>&nbsp;<span class="keyword">of</span>&nbsp;<span class="constructor">Parsetree</span>.extension<br>
&nbsp;&nbsp;<span class="keyword">and</span>&nbsp;class_field_kind&nbsp;=<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="constructor">Cfk_virtual</span>&nbsp;<span class="keyword">of</span>&nbsp;<span class="constructor">Parsetree</span>.core_type<br>
&nbsp;&nbsp;&nbsp;&nbsp;<s