I think that there is an error in this section of the manual. It tells you to include a placeholder
<$include>
If you include the backslash at the beginning of the placeholder, it stops it from working. The placeholder should be:-
<$include>
This should be fixed in the 3.0.1 revision, available for download from the support page.
The problem originates from the fact that when you write about placeholders in Scrivener, you need a way to make it so you can talk about them without them actually doing the things they are meant to do during compile. 
So in most cases you want to type in <$label> or whatever—but there is one exception: if the placeholder wouldn’t resolve to anything then it isn’t treated as one and the backslash becomes redundant. In this case, I was referring to <$include> tags that weren’t actually linked to anything, so they were already inert and didn’t need to be escaped.