the source in
http://www.lilypond.org/doc/v2.17/Documentation/snippets/vocal-music#vocal-music-vertically-centered-common-lyrics
starts with
\include "english.ly"
leftbrace = \markup { \override #'(font-encoding . fetaBraces) \lookup
#"brace240" }
rightbrace = \markup { \rotate #180 \leftbrace }
I think these lines should be skipped since neither English note names nor
left braces are used afterwards (or the leftbrace and rightbrace should be
used!)
and I object to the 1st sentence:
"In a vocal piece where there are several (two,four or more) lines of
lyrics, and common lyrics for all voices at some point, these common
lyrics
may be vertically centered regardingly, as shown in the following
example:"
no (vertical) centering is done - it just positions the line with
extra-offset 5 spaces lower.