Re: Doc: simplify example for unpure-pure containers (issue 5623044)

[plroskin]

To be honest, there are many things I don't understand.  In fact, I
reduced the example to understand it better.

Why is horizontal spacing affected even though the purity affects the
Y-axis only?  Why do stems fix the spacing?  Why doesn't this cause the
spacing problem:

  \override NoteHead #'text = \markup { "o" }
  \override NoteHead #'stencil = #ly:text-interface::print

But this does cause the problem:

  \override NoteHead #'text = \markup { "o" }
  \override NoteHead #'stencil =
   #(lambda (grob) (ly:text-interface::print grob))

Cannot it happen a simple change would make Lilypond recognize lambda
expressions as pure functions, breaking this example?  Maybe I removed
some future-proofing?

Perhaps some answers to those questions could be used to improve the
documentation.

http://codereview.appspot.com/5623044/