define line break

[MING TSANG]

According to lilypond usage 5.2

• Define mBreak = { \break } and insert \mBreak in the input file whenever the manuscript has a line break. This makes it much easier to compare the LilyPond music to the original music. When you are finished proofreading your score, you may define mBreak = { } to remove all those line breaks. This will allow LilyPond to place line breaks wherever it feels are best.

I coded:
\version 2.13.61
define mBreak = {\break}  
\relative c, { c d e f g a b \mBreak b b a a }

I got the following error:
C:/Documents and Settings/Administrator/Desktop/LILY_POND/little-dream.ly:16:7: error: syntax error, unexpected STRING, expecting SCM_IDENTIFIER or SCM_TOKEN or '='
define
       mBreak = {\break}


Question:  what is the correct syntax?