diff --git a/wpa_supplicant/doc/docbook/wpa_supplicant.sgml b/wpa_supplicant/doc/docbook/wpa_supplicant.sgml
index de3409d76..84f59908b 100644
--- a/wpa_supplicant/doc/docbook/wpa_supplicant.sgml
+++ b/wpa_supplicant/doc/docbook/wpa_supplicant.sgml
@@ -327,11 +327,15 @@
 
   <refsect1>
     <title>Command Line Options</title>
+    <para>Most command line options have global scope. Some are given per
+    interface, and are only valid if at least one <option>-i</option> option
+    is specified, otherwise they're ignored. Option groups for different
+    interfaces must be separated by <option>-N</option> option.</para>
     <variablelist>
       <varlistentry>
 	<term>-b br_ifname</term>
 	<listitem>
-	  <para>Optional bridge interface name.</para>
+	  <para>Optional bridge interface name. (Per interface)</para>
 	</listitem>
       </varlistentry>
 
@@ -345,35 +349,40 @@
       <varlistentry>
 	<term>-c filename</term>
 	<listitem>
-	  <para>Path to configuration file.</para>
+	  <para>Path to configuration file. (Per interface)</para>
 	</listitem>
       </varlistentry>
 
       <varlistentry>
 	<term>-C ctrl_interface</term>
 	<listitem>
-	  <para>Path to ctrl_interface socket (only used if -c is not).</para>
+	  <para>Path to ctrl_interface socket (Per interface. Only used if
+		  <option>-c</option> is not).</para>
 	</listitem>
       </varlistentry>
 
       <varlistentry>
 	<term>-i ifname</term>
 	<listitem>
-	  <para>Interface to listen on.</para>
+	  <para>Interface to listen on. Multiple instances of this option can
+	  be present, one per interface, separated by <option>-N</option>
+	  option (see below).</para>
 	</listitem>
       </varlistentry>
 
       <varlistentry>
 	<term>-d</term>
 	<listitem>
-	  <para>Increase debugging verbosity (-dd even more).</para>
+	  <para>Increase debugging verbosity (<option>-dd</option> even
+		  more).</para>
 	</listitem>
       </varlistentry>
 
       <varlistentry>
 	<term>-D driver</term>
 	<listitem>
-	  <para>Driver to use.  See the available options below.</para>
+	  <para>Driver to use. (Per interface, see the available options
+		  below.)</para>
 	</listitem>
       </varlistentry>
 
@@ -387,7 +396,8 @@
       <varlistentry>
 	<term>-g global ctrl_interface</term>
 	<listitem>
-	  <para>Path to global ctrl_interface socket.</para>
+	  <para>Path to global ctrl_interface socket. If specified, interface
+	  definitions may be omitted.</para>
 	</listitem>
       </varlistentry>
 
@@ -422,7 +432,7 @@
       <varlistentry>
 	<term>-p</term>
 	<listitem>
-	  <para>Driver parameters.</para>
+	  <para>Driver parameters. (Per interface)</para>
 	</listitem>
       </varlistentry>
 
@@ -436,14 +446,16 @@
       <varlistentry>
 	<term>-q</term>
 	<listitem>
-	  <para>Decrease debugging verbosity (-qq even less).</para>
+	  <para>Decrease debugging verbosity (<option>-qq</option> even
+		  less).</para>
 	</listitem>
       </varlistentry>
 
       <varlistentry>
 	<term>-u</term>
 	<listitem>
-	  <para>Enabled DBus control interface.</para>
+	  <para>Enabled DBus control interface. If enabled, interface
+	  definitions may be omitted.</para>
 	</listitem>
       </varlistentry>