Difference between #music and \music?

[David F.]

The following code runs without error:

%%%%
\version "2.19"

#(define-markup-command (myMarkup layout props music)
  (ly:music?)
    % Code to generate markup based on music goes here—elided for simplicity
    (interpret-markup layout props "myMarkup"))

music = { c'1 }

\markup \myMarkup #music

\ music
%%%%

However, if I replace #music with \music as the argument to \myMarkup, I get 
the following error:

document.ly:9:19: error: syntax error, unexpected MUSIC_IDENTIFIER, expecting 
LOOKUP_IDENTIFIER or SCM_FUNCTION or SCM_IDENTIFIER or SCM_TOKEN
\markup \myMarkup 
                  \music

Can anyone shed some light on the difference between #music and \music?

Thanks,
David