Allow specifying line numbers in 'editor'. Take advantage in <C-i> and view-source links.

common/locale/en-US/options.xml

@@ -69,6 +69,25 @@
     </dd>
 </dl>
 
+<p tag="format-string">
+    Some options may be given format strings containing %-delimited escape
+    sequences. Character sequences in the form of <em>%</em><a>character</a> are
+    substituted by a specified replacement string. If <a>character</a> is
+    upper-case, then the string is automatically
+    <link topic="quoting">quoted</link>. Any substring enclosed by <em>%[</em>
+    and <em>%]</em> is automatically elided if any of the contained format
+    characters aren't currently valid. A literal <em>%</em> character may be
+    included with the special escape sequence <em>%%</em>.
+</p>
+
+<p>
+    For example, given the format string <str>%[(cmd: %c) %]%[line: %l %]%F</str>,
+    where <em>l</em>=<hl key="Number">32</hl> and
+    <em>f</em>=<str delim="'">Lieder eines fahrenden Gesellen.txt</str>,
+    the result is formatted as
+    <str>line: 32 'Lieder eines fahrenden Gesellen.txt'</str>
+</p>
+
 <h2 tag="set-option E764">Setting options</h2>
 
 <item>
@@ -544,6 +563,19 @@
             other commands which launch an external text editor.
         </p>
 
+        <p>
+            Accepts a <t>format-string</t> with the following escapes available.
+            Arguments containing escapes which are not relevant to a given call
+            are automatically elided. All field splitting is done before format
+            characters are processed.
+        </p>
+
+        <dl>
+            <dt>%f</dt> <dd>The file to edit. Appended as the final argument if missing.</dd>
+            <dt>%l</dt> <dd>The line number at which to position the cursor.</dd>
+            <dt>%c</dt> <dd>The column at which to position the cursor.</dd>
+        </dl>
+
         <warning>
             &dactyl.appName; will not behave correctly if the editor forks its
             own process rather than blocking until editing is complete. Gvim