Index: trunk/doc/user/06_features/hierarchic/index.html
===================================================================
--- trunk/doc/user/06_features/hierarchic/index.html	(revision 10193)
+++ trunk/doc/user/06_features/hierarchic/index.html	(revision 10194)
@@ -201,12 +201,76 @@
 under the module's root sheet will see the object, but it will not
 merge with anything above the module's subtree.
 <p>
-TODO: example
+In example <a href="../../../examples/hierarchic/32_subtree/">32_subtree</a>
+an extension of the 24_led example: the whole led control section with the
+microcontrolled and the two LEDs are packed into a subtree. The root of the
+subtree is led_ctrl.rs and is almost the same circuit as main.rs in
+24_led. The change is that the 2-channel MCU controlled LED subtree is now
+commanded through SPI.
 <p>
-TODO:
-	- describe the example once the net names are known
-	- explain how auto is searching
+A new root sheet is added on top, called main.rs, which adds U5, the main
+microcontroller, then creates two instances of the led control subtree and
+hooks up U5's SPI to control both led_ctrl microcontrollers (using different
+slave select signals).
+<p>
+Sheet instance tree will look like:
+<pre>
+main.rs (SPI master)
+ |
+ +- S1: led_ctrl.rs (SPI slave 2 channel LED control)
+ |  |
+ |  +- S1/S1: led.rs (LED and FET)
+ |  |
+ |  +- S1/S2: led.rs (LED and FET)
+ |
+ +- S2: led_ctrl.rs (SPI slave 2 channel LED control)
+    |
+    +- S2/S1: led.rs (LED and FET)
+    |
+    +- S2/S2: led.rs (LED and FET)
+</pre>
 
+<p>
+The expert feature, subtree net, can be observed on sheet led_ctrl.rs. It's
+the v/blink_enable net. This used to be a global net in example 24_led, so
+that it didn't need to have a dedicated terminal on the sheet ref syms. In
+this example we need the same, except that blink_enable can not be fully global
+because then the two led_ctrl sheets (S1 and S2) would share the same led_ctrl
+net. What is needed instead is a <i>subtree local network</i>, which means that
+on the level of S1 and S2 these are two separate networks, but in the subtree
+under S1 and in the other subtree under S2 the network is accessible without
+having to use sheet terminals.
+<p>
+The practical implementation is:
+<ul>
+	<li> on the top of the subtree, on led_ctrl.rs, the net is referenced with the
+	     v/ prefix, which means it's a subtree net: visible downward but isn't merged
+	     upward
+	<li> on subsheets under led_ctrl.rs, the net is referenced with the ^/ prefix,
+	     which means the net is search upward, preferring a subtree local net and
+	     not a project global nets.
+	<li> the rest of the nets are the same as before:
+	<ul>
+		<li> global nets like Vcc or gnd or V9V
+		<li> sheet local nets like ./res_led (which will have 4 instances, named like S1/S2/res_led)
+		<li> nets passed through sheet ref sym terminals to the child sheet's sheet terminal
+	</ul>
+</ul>
+<p>
+Note: on led_ctrl.rs it's possble to name the blink_enable net without any prefix
+and the example will still work. This is because of the search preference of
+the <i>auto</i> scope that is used when the name is not prefixed: it will
+first search sheet local nets to bind to then starts ascending level by level
+looking for a subtree local net, bumping into the same v/blink_enable on
+led_ctrl.rs. However, if the search fails (e.g. led_ctrl.rs fails to offer
+a subtree local net named blink_enable), the <i>auto</i> will silently create
+a global net whereas the ^/ prefixed name will throw an error, which is a
+safer choice.
+
+
+<h4 autotoc="yes"> Expert: component addressing </h4>
+
+
 <h4 autotoc="yes"> Expert: addressing by path </h4>
 <p>
 Not yet supported. (TODO)