-<p>The Packet interface assumes that headers have a fixed size.
-It is difficult to return a pointer into the data region when its
-position will only be known once the header values are bound.</p>
-<p>Generally, an incoming call to the Packet interface of a protocol
-has an accompanying outgoing call to the Packet interface of the
-component below it. The one exception to this is the data link
-layer. For example, if there is a network that introduces
-16-bit sequence numbers to packets, it might look like this:</p>
+<p>The Packet interface assumes that headers have a fixed size. It is
+difficult to return a pointer into the data region when its position
+will only be known once the header values are bound.</p>
+<p>The <tt class="docutils literal"><span class="pre">clear</span></tt> command clears out all headers, footers, and metadata
+for lower layers. For example, calling <tt class="docutils literal"><span class="pre">clear</span></tt> on a routing
+component, such as CollectionSenderC[4]_, will clear out the
+collection headers and footers. Furthermore, CollectionSenderC will
+recursively call <tt class="docutils literal"><span class="pre">clear</span></tt> on the layer below it, clearing out the
+link layer headers and footers. Calling <tt class="docutils literal"><span class="pre">clear</span></tt> is typically
+necessary when moving a packet across two link layers. Otherwise, the
+destination link layer may incorrectly interpret metadata from the
+source link layer, and, for example, transmit the packet on the wrong
+RF channel. Because <tt class="docutils literal"><span class="pre">clear</span></tt> prepares a packet for a particular link
+layer, in this example correct code would call the command on the
+destination link layer, not the source link layer.</p>
+<p>Typically, an incoming call to the Packet interface of a protocol has
+an accompanying outgoing call to the Packet interface of the component
+below it. The one exception to this is the data link layer. For
+example, if there is a network that introduces 16-bit sequence numbers
+to packets, it might look like this:</p>