newbie: manual 2.2.1, staves, \clef command

[ed stuckems]

Hello everyone.  Can someone please explain why the \clef command
seems to override simultaneous music in the following situation?

Before getting to a specific example, I'd like to draw attention to
the following excerpt from section 2.2.1 of the manual:

"To determine the number of staves in a piece, LilyPond looks at the
beginning of the first expression. If there is a single note, there is
one staff; if there is a simultaneous expression, there is more than
one staff."

This would appear to be the case in the following:

<<
 { f a c e }
 { e g b d }
>>

However, if a \clef is specified, the statement doesn't appear to
hold.  For example, the following doesn't produce multiple staves
despite the fact that the beginning of the first expression starts
with simultaneous expression like the example above:

<<
 { f a c e }
 { \clef "bass" e g b d }
>>

In this case, both expressions are placed on one staff beginning with
a bass clef.  I infer that there something special about the use of
\clef that causes lilypond to re-examine the multiple staves vs single
staff assessment. When I looked up the \clef command, there was
nothing that indicates the command has side effects.

In order to get the two staves, you must prefix each expression with a
\new Staff as in the following:

<<
 \new Staff { f a c e }
 \new Staff { \clef "bass" e g b d }
>>

So my question is "why does adding the \clef also require adding the
"\new Staff" when section 2.2.1 suggests otherwise?"  What have I
missed?

regards,
eds