anchor.diff:  <div class="radio">
     <label>
       <input name="assignment[teamset_plan]" id="teamset_clone" type="radio"
  -           value="clone">
  +           value="clone" <% if asgn.teamset_plan == "clone" %>checked<% end %>>
       <strong>Clone existing teamset:</strong> clone the teamset that
       this assignment currently shares with another one, so that changes
       to the teamset for this assignment will not affect the previous
  
positive.code: <div class="radio">
    <label>
      <input name="assignment[teamset_plan]" id="teamset_copy" type="radio"
             value="copy">
      <strong>Copy existing teamset:</strong> clones the teams from an existing
      teamset, so changes to one set will not affect the other.
      <% if @legal_actions[:copy][:existing] %>
  
negative.code:     will be ignored.
      <br>
      <%= select_tag "assignment[teamset_source_copy]",
          options_from_collection_for_select(course.teamsets, "id", "name", asgn.teamset_source_copy&.to_i),
          prompt: [asgn.teamset_source_copy,
                   "Choose an existing teamset"].find(&:presence),
          class: "col-sm-12" %>
    </label>
  </div>
  