switching from a "real" dir to an external, and vice versa

[Robert P. J. Day]

   based on a recent discussion on the main SVN mailing list, it's not  
clear how one replaces an existing versioned directory with an  
external, and vice versa.  in fact, i've had to do this a few times  
over the last several days, as a repo i'm working with duplicates  
content already in another repo, so i've replaced a number of physical  
directories with externals.

   however, the book section on "externals" doesn't describe how to do  
this operation in a single commit (which, logically, it should be,  
no?).  i would think that this is a reasonably common operation, but i  
had to do it in two steps each time to avoid getting a conflict or a  
complaint from subversion.

   also, as time went by, i had to *undo* some of those externals, and  
replace them with the corresponding physical dir when it became  
obvious that the two dirs were going to go their separate ways and,  
again, i needed to do it in two operations when i really wanted that  
change to be represented by a single commit.

   would it be possible for the "externals" section to explain how  
this should be done properly?  thanks.

rday