diff --git a/src/doc/doc/about/drc_ref_source.xml b/src/doc/doc/about/drc_ref_source.xml
index 734fe6df7..a746917e3 100644
--- a/src/doc/doc/about/drc_ref_source.xml
+++ b/src/doc/doc/about/drc_ref_source.xml
@@ -181,15 +181,21 @@ Filters are expressions describing ranges
 of layers and/or datatype numbers or layer names. Multiple filters
 can be given and all layers matching at least one of these filter
 expressions are joined to render the input layer for the DRC engine.
+For the syntax of the filter expressions see <class_doc href="LayerMap#map">LayerMap#map</class_doc> (look for
+the version that uses a map expression).
 </p><p>
 Some filter expressions are:
 </p><p>
 <ul>
 <li><tt>1/0-255 </tt>: Datatypes 0 to 255 for layer 1 </li>
+<li><tt>1/* </tt>: All datatypes for layer 1 </li>
+<li><tt>1/0,5,10 </tt>: Datatypes 0, 5 and 10 for layer 1 </li>
+<li><tt>1/0;2/17 </tt>: Layer 1, datatype 0 and layer 2, datatype 17 </li>
 <li><tt>1-10 </tt>: Layers 1 to 10, datatype 0 </li>
 <li><tt>METAL </tt>: A layer named "METAL" </li>
-<li><tt>METAL (17/0) </tt>: A layer named "METAL" or layer 17, datatype 0 (for GDS, which does
-not have names)</li>
+<li><tt>METAL;VIA </tt>: A layer named "METAL" and the layer named "VIA" </li>
+<li><tt>METAL;17/0 </tt>: A layer named "METAL" and layer 17, datatype 0 </li>
+<li><tt>'17' </tt>: A layer named "17". Note the quotes which indicate a string, not a layer number </li>
 </ul>
 </p><p>
 Layers created with "input" may contain both texts (labels) and polygons. There is a subtle
diff --git a/src/drc/drc/built-in-macros/_drc_source.rb b/src/drc/drc/built-in-macros/_drc_source.rb
index 8e9a42562..1ada0540e 100644
--- a/src/drc/drc/built-in-macros/_drc_source.rb
+++ b/src/drc/drc/built-in-macros/_drc_source.rb
@@ -383,15 +383,21 @@ def extent(cell_filter = nil)
     # of layers and/or datatype numbers or layer names. Multiple filters
     # can be given and all layers matching at least one of these filter
     # expressions are joined to render the input layer for the DRC engine.
+    # For the syntax of the filter expressions see RBA::LayerMap#map (look for
+    # the version that uses a map expression).
     #
     # Some filter expressions are:
     #
     # @ul
     # @li @tt 1/0-255 @/tt: Datatypes 0 to 255 for layer 1 @/li
+    # @li @tt 1/* @/tt: All datatypes for layer 1 @/li
+    # @li @tt 1/0,5,10 @/tt: Datatypes 0, 5 and 10 for layer 1 @/li
+    # @li @tt 1/0;2/17 @/tt: Layer 1, datatype 0 and layer 2, datatype 17 @/li
     # @li @tt 1-10 @/tt: Layers 1 to 10, datatype 0 @/li
     # @li @tt METAL @/tt: A layer named "METAL" @/li
-    # @li @tt METAL (17/0) @/tt: A layer named "METAL" or layer 17, datatype 0 (for GDS, which does
-    #           not have names)@/li
+    # @li @tt METAL;VIA @/tt: A layer named "METAL" and the layer named "VIA" @/li
+    # @li @tt METAL;17/0 @/tt: A layer named "METAL" and layer 17, datatype 0 @/li
+    # @li @tt '17' @/tt: A layer named "17". Note the quotes which indicate a string, not a layer number @/li
     # @/ul
     #
     # Layers created with "input" may contain both texts (labels) and polygons. There is a subtle