[css3-background] Delimiter character in the new background color fallback syntax

In this new syntax, I'm noticing that a forward slash is used as the  
delimiter. However on other fallback schemes such as inserting and  
replacing content with the 'content' property (http://www.w3.org/TR/css3-content/#content 
) and 'font-family' fallback, we're using a comma as the delimiter.

Just for my own clarity, could someone explain to me why it's been  
decided to use a forward slash as the delimiter in this instance?

James