regressions: confusion? glissando.ly

[Stan Sanderson]

regressions: glissando.ly text reads, "The engraver does no time- 
keeping, so it involves some trickery to get << { s8 s8 s4 } { c4  
\gliss d4 } >> working correctly."

How does it relate to the snippet? Also, the snippet appears to  
render correctly with out the voice and stem direction definitions;  
as follows:

\layout{
  line-width = 50.\mm
  indent = 0
}

\new Staff \relative c''{
  \override Glissando #'breakable = ##t
    %% gliss non gliss and
  c4 \glissando d e \glissando f \glissando \break
  %% consecutive
  c \glissando d, \glissando e'
  << { e8 \glissando g8 }
         \\ { \repeat unfold 4 d16 } >> \break
  \override Glissando  #'style = #'zigzag
  c4 \glissando c,, \glissando c' \glissando d
}


Stan