Well, I define the term in the first part of the document:

>> The term "URL-safe" implies a string which does not contain any characters *forbidden* in
[RFC 1738][]. The word "slugify" refers to the process of producing a URL-safe string 
from a given source string.

The actual part of the RFC is **2.2 URL Character encoding issues**. Maybe I should make explict mention to that.

The "/" chacracter is classed as *unsafe* in the RFC.