after-title-spacing: "space" includes title

[Mark Polesky]

NR 4.1.2 "Page formatting - Vertical dimensions" says...

after-title-spacing:
  space – the amount of stretchable space between the
  baseline of a title and the center of the staff that
  follows it;

But compiling a test file with annotate-spacing suggests
that the "space" is measured from the *top* of a title, not
the *baseline*.  Before someone jumps to change the
Documentation to match the function, I'd like to know the
rationale.  It seems measuring "after-title-spacing" should
really start from the baseline.

- Mark

ps. here's a test file:

\version "2.13.35"

\header {
  title = "Title"
}

\paper {
  after-title-spacing = #'((space . 10) (padding . 0.5))
  annotate-spacing = ##t
  ragged-right = ##f
}

\new Voice {
  \repeat unfold 8 { c''2 c'' }
}