Document the "editor command" feature more fully.

* en/book/ch07.xml
  (svn.advanced.confarea.opts.config): Specify how Subversion finds an
    editor, how the editor command string is used, and how the editor
    should behave.

* en/book/ch09.xml
  (svn.ref.svn.sw): Add a cross-reference from "--editor-cmd" to the above.

Index: en/book/ch07.xml
===================================================================
--- en/book/ch07.xml	(revision 2082)
+++ en/book/ch07.xml	(working copy)
@@ -482,12 +482,35 @@
                 user wishes to edit, and the edits take place right
                 in the editor program (see <xref
                 linkend="svn.advanced.props" />).  This option's default
-                value is empty.  If the option is not set, Subversion
-                will fall back to checking the environment variables
-                <literal>SVN_EDITOR</literal>,
-                <literal>VISUAL</literal>, and
-                <literal>EDITOR</literal> (in that order) for an
-                editor command.</para>
+                value is empty.  The order of priority for determining the
+                editor command is:</para>
+              <orderedlist>
+                <listitem>
+                  <para>Command-line option <literal>--editor-cmd</literal></para>
+                </listitem>
+                <listitem>
+                  <para>Environment variable <literal>SVN_EDITOR</literal></para>
+                </listitem>
+                <listitem>
+                  <para>Configuration option <literal>editor-cmd</literal></para>
+                </listitem>
+                <listitem>
+                  <para>Environment variable <literal>VISUAL</literal></para>
+                </listitem>
+                <listitem>
+                  <para>Environment variable <literal>EDITOR</literal></para>
+                </listitem>
+                <listitem>
+                  <para>Possibly, a default value built in to Subversion
+                    (not present in the official builds)</para>
+                </listitem>
+              </orderedlist>
+              <para>The value of any of these options or variables is
+                (unlike <literal>diff-cmd</literal>) the beginning of a
+                command line to be executed by the shell.  Subversion
+                appends a space and the pathname of the temporary file to be
+                edited.  The editor should modify the temporary file and
+                return a zero exit code to indicate success.</para>
             </listitem>
           </varlistentry>
           <varlistentry>
Index: en/book/ch09.xml
===================================================================
--- en/book/ch09.xml	(revision 2082)
+++ en/book/ch09.xml	(working copy)
@@ -108,7 +108,9 @@
             <replaceable>CMD</replaceable></term>
           <listitem>
             <para>Specifies an external program to use to edit a log message
-              or a property value.</para>
+              or a property value. See the <literal>editor-cmd</literal>
+              section in <xref linkend="svn.advanced.confarea.opts.config"/>
+              for ways to specify a default editor.</para>
           </listitem>
         </varlistentry>
       
