Hi, all!
What about unifying "\paper" and "\layout" into a single "\layout"
directive, such that in the input language there is no syntactical
difference any more between \paper and \layout block? (Of course, in the
implementation, the different scopes still could be kept.) Then the place
where the \layout occurs in the .ly file determines which properties can
be changed (that is exactly what scopes are about).
Obviously, if someone operates in the wrong scope, i.e. if someone tries
to change things on score level \layout block which only should be changed
globally (such as paper margin), lily should emit a warning.