PR Stanley wrote: Just a meta-point. The dash-dash-space sequence introduces a signature. If you write your reply after the dash-dash-space, as you did here, a lot of us won't see your reply because we have our mail/news clients set up to ignore signatures. I had to view the original message source to see what was going on. As for the main point, you can look at it as a substitution; it's just that you have to jump through some hoops to think of it as substituting plain text. For example, put parentheses around the bit that's been substituted. A slightly more accurate model would be to view things as substitution of parse trees. Then one can point out that instead of doing straight substitution, what actually happens is that subexpressions are shared. But that only effects performance; the observable behavior is the same as if you did substitution (of parse trees, or of text but adding the parentheses in the right places).