Difference between # and $

[Urs Liska]

Hi,

I have a hard time to understand the difference between # and $ in 
LilyPond code blocks within Scheme functions.

2.2.1 of the Extending manual says:
"Within LilyPond code blocks, use # to reference function arguments 
(eg., ‘#arg1’) or to start an inline Scheme expression containing 
function arguments (eg., ‘#(cons arg1 arg2)’). Where normal Scheme 
expressions using # don’t do the trick, you might need to revert to 
immediate Scheme expressions using $, for example as ‘$music’."

This doesn't really help.

2.1. says:
"... can deal with embedded Scheme expressions starting with $ and #."

This is even less helpful.

Please give me a meaningful explanation of what "immediate Scheme 
expressions" are and when and why you should use them. Then I may be 
able to update the docs.

Urs