Suggestion: mention up front that external URLs must name directories

[Eric Hanchrow]

I often see people on #svn who are surprised that they cannot create
a svn:externals property whose value is a file.  I think this change
would alleviate that confusion:

Index: ch-advanced-topics.xml
===================================================================
--- ch-advanced-topics.xml	(revision 2624)
+++ ch-advanced-topics.xml	(working copy)
@@ -2321,7 +2321,7 @@
       <firstterm>externals definitions</firstterm>.  An externals
       definition is a mapping of a local directory to the
       URL—and possibly a particular revision—of a
-      versioned object.  In Subversion, you declare externals
+      versioned directory.  In Subversion, you declare externals
       definitions in groups using the <literal>svn:externals</literal>
       property.  You can create or modify this property using
       <command>svn propset</command> or <command>svn

-- 
Keaton, Chaplin, Garbo - let them now make room for Gromit.
        A. O. Scott, in The New York Times