NR 1.7.2 - snippet "Analysis brackets with labels"

[Federico Bruni]

Can you please clarify the last sentence of this snippet:

http://lilypond.org/doc/v2.19/Documentation/notation/outside-the-staff.html#analysis-brackets


\layout {
 \context {
   \Voice
   \consists "Horizontal_bracket_engraver"
   \override HorizontalBracket.direction = #UP
 }
}

{
 \once\override HorizontalBracketText.text = "a"
 c''\startGroup d''\stopGroup
 \once\override HorizontalBracketText.text = "a'"
 e''\startGroup d''\stopGroup
 c''
 -\tweak text \markup \bold \huge "b" \startGroup
 -\tweak text "a" \startGroup
 d''\stopGroup
 e''-\tweak text "a'" \startGroup
 d''\stopGroup\stopGroup
 c''-\tweak text foo \startGroup d'' e'' f''
 \break
 g'' a'' b'' c'''\stopGroup
}


"""
Analysis brackets with labels

Text may be added to analysis brackets through the text property of the 
HorizontalBracketText grob. Adding different texts to brackets 
beginning at the same time requires the \tweak command. Bracket text 
will be parenthesized after a line break.
"""

Bracket text will be parenthesized after a line break.

It cannot simply mean that HorizontalBracketText can break a line (the 
parenthesis will be closed after the line break). So what else is 
trying to say?

Another question: why the markups added using "\tweak text" are not 
printed? (bars 2, 3 and 4)

Thanks in advance
Federico