Index: index.html
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--- index.html	(revision 31794)
+++ index.html	(revision 31795)
@@ -173,6 +173,7 @@
 	<tr><th> layer group attribute name <th> description
 	<tr><td> thickness                  <td> thickness of the physical layer, given with unit (e.g. 0.2mm or 200um or 50mil)
 	<tr><td> <i>plugin</i>::thickness   <td> overrides the above thickness value for a specific plugin, if the plugin supports it; for example openems::thickness will use a different layer group thickness for the given layer group when exporting to openems
+	<tr><td> dielectric                 <td> Relative dielectric constant, typically for substrate layer groups, Er (unitless)
 </table>
 <p>