title: Remove svn:externals property from a folder
body: <p>I have a branch of the trunk. I need to re-set the properties of the externals in the branch to a different point.
  My idea was to remove them all and re-set them with propset.
  When I type <code>svn propdel svn:externals http://path-to-branch/externals</code></p>
  
  <p>I get </p>
  
  <blockquote>
    <p>svn: E200009: Targets must be working copy paths</p>
  </blockquote>
  
  <p>Whats the problem with my command?</p>