diff --git a/src/lay/lay/doc/about/drc_ref_global.xml b/src/lay/lay/doc/about/drc_ref_global.xml
index 917ada706..96c622861 100644
--- a/src/lay/lay/doc/about/drc_ref_global.xml
+++ b/src/lay/lay/doc/about/drc_ref_global.xml
@@ -306,6 +306,8 @@ clip(0.mm, 0.mm, 0.5.mm, 0.6.mm)
 # shapes now will be taken from the given rectangle and clipped to it
 l1 = input(1, 0)
 </pre>
+</p><p>
+To remove the clip condition, call "clip" without any arguments.
 </p>
 <a name="connect"/><h2>"connect" - Specifies a connection between two layers</h2>
 <keyword name="connect"/>
@@ -619,11 +621,12 @@ actual edges from the first input (see <a href="#separation">separation</a> for
 <p>
 Similar to <a href="#log">log</a>, but the message is printed formatted as an error
 </p>
-<a name="extent"/><h2>"extent" - Creates a new layer with the bounding box of the default source</h2>
+<a name="extent"/><h2>"extent" - Creates a new layer with the bounding box of the default source or cell bounding boxes</h2>
 <keyword name="extent"/>
 <p>Usage:</p>
 <ul>
 <li><tt>extent</tt></li>
+<li><tt>extent(cell_filter)</tt></li>
 </ul>
 <p>
 See <a href="/about/drc_ref_source.xml#extent">Source#extent</a> for a description of that function.
diff --git a/src/lay/lay/doc/about/drc_ref_source.xml b/src/lay/lay/doc/about/drc_ref_source.xml
index 05525f41e..20a46bee9 100644
--- a/src/lay/lay/doc/about/drc_ref_source.xml
+++ b/src/lay/lay/doc/about/drc_ref_source.xml
@@ -96,18 +96,31 @@ Use the global version of "edges" without a source object to address the default
 </p><p>
 This method has been introduced in version 0.27.
 </p>
-<a name="extent"/><h2>"extent" - Returns a layer with the bounding box of the selected layout</h2>
+<a name="extent"/><h2>"extent" - Returns a layer with the bounding box of the selected layout or cells</h2>
 <keyword name="extent"/>
 <p>Usage:</p>
 <ul>
 <li><tt>source.extent</tt></li>
+<li><tt>source.extent(cell_filter)</tt></li>
 </ul>
 <p>
+Without an argument, the extent method returns a layer with the bounding box
+of the top cell. With a cell filter argument, the method returns a layer
+with the bounding boxes of the selected cells. The cell filter is a glob
+pattern.
+</p><p>
 The extent function is useful to invert a layer:
 </p><p>
 <pre>
 inverse_1 = extent.sized(100.0) - input(1, 0)
 </pre>
+</p><p>
+The following example returns the bounding boxes of all cells whose
+names start with "A":
+</p><p>
+<pre>
+a_cells = extent("A*")
+</pre>
 </p>
 <a name="global_transform"/><h2>"global_transform" - Gets or sets a global transformation</h2>
 <keyword name="global_transform"/>