Documentation clarification?

[Geoff Horton]

(Sorry to keep hammering on the docs--I'm working on a project that requires me
to look at them closely and I keep finding stuff.)

2.7.38, section 8.2.8, dealing with different editions and the \tag command:

Toward the bottom of the section (p. 196 of the PDF), right above "See Also", it
says: "The argument of the \tag command should be a symbol." I just successfully
used \tag with \override commands, and I read "symbol" as referring to something
that actually prints on the output page.

E.g., the following works and I didn't think it should, based on the docs:
optSlur = \tag #'withSlur { \once \override Slur #'transparent = ##t }

soprano = \relative c'' {
  \optSlur
  c4( c) c( c) \bar "|."
}

I can then show the slur or hide it with the \removeWithTag command.

Geoff