> I consider it bizarre that the top-level variable `output-filename`
> is only considered in a `\book` block where the paper variable
> `output-suffix` is also set, contrary to `output-suffix`. Why is
> `output-filename` considered at all? Where in the code is this
> read? AFAIK, top-level variables are read with `ly:parser-lookup`,
> and I can't find this for `output-filename`.
>
> Or is this an inheritance thing? Does a `\book` block inherit all
> top-level expressions and convert them to paper variables?
Some debugging shows it seems to be the latter: All top-level
definitions are available as paper variables within a book's paper
block, together with all paper variables of the top-level paper block:
Executing
```
foo = "FOO"
\paper {
bar = "BAR"
}
\book {
#(ly:message "paper variable 'foo': ~a\n"
(paper-variable $current-book 'foo))
#(ly:message "paper variable 'bar': ~a\n"
(paper-variable $current-book 'bar))
{ c' }
}
```
yields
```
paper variable 'foo': FOO
paper variable 'bar': BAR
```
Is this really intentional?
Werner
