What is the difference between \paper and \layout blocks?

[David Kastrup]

What should it be?

The presence of a \layout block in a score makes for typeset output.
\paper contains things like paper dimensions only necessary for typeset
output.  Also base file names that are also relevant for MIDI.

Global markup currently only gets to see the \paper block.  That also
concerns things like \score markup that can get information for
typesetting from \layout blocks.

Layout blocks "inherit" from the paper block: when a variable in a
layout block is not set, it is taken from the respective paper block.

Currently a "paper-book" where the typesetting is done only stores the
relevant paper block.  Consequently, any page-level/top-level markup
currently gets only the paper block as its "layout" parameter.

That is not accepted as layout block in a score markup.

Suggestions?

-- 
David Kastrup