A visible stencil for a NoteColumn grob

[Paolo Prete]

Hello. 

1) How can  I associate a stencil to a NoteColumn grob?

I would like to show a vertical line in correspondence of it, but it seems that

\override NoteColumn.stencil ... has no effect.

2) is it possible to associate an output-attributes list to the NoteColumn grob, as well (so that it appears on the corresponding svg tag)?

I don't mean a property of the NoteHead, or Stem etc.: I mean a property of the NoteColumn (invisible) grob

http://lilypond.org/doc/v2.19/Documentation/internals/notecolumn

Thanks,

Paolo