dl semantically associates selector name with values

Select from existing tags.
Use Control/Command/Shift keys to select multiple tags. Type-to-skip functionality with javascript enabled could be described as "Hover and type the first letter to skip through tags." However, on touch-driven devices, vertical hover typically scrolls the page, so horizontal hover is necessary to enable this. Alternatively, clicking any of the tags also enables type-to-skip. So the help could technically be extended to handle this special case as "Hover or click and type the first letter to skip through tags.", but I think this would be confusing to the majority of users. The decision at this point is to not try to explain any of this on the page.
These spans are hidden by css, and used by the JavaScript called below. No tags currently selected. % tags currently selected. Call js to modify this widget with both a scrollbar and checkboxes. There may be a better place to put this js call; examples exist in others' widget.py and js files, but having it here covers cases where some but not all select elements call js to be modified. Todo: The #subject should eventually refer to the template variable.
An existing tag

Create and apply new tags.
Enter one tag per line, multiple words allowed.
  A new tag