title: How do I indicate collate order in Roxygen2?
body: <p>Using roxygen2 documentation with devtools <code>document</code> function automatically generates a <code>Collate:</code> field in the package DESCRIPTION, regardless of whether or not it is necessary to load the package library files in a particular order.</p>
  
  <p>I'm working on a package with a bunch of S4 methods and want to be sure the class definitions are loaded before any methods or other classes using them, which I understand I can do with the <code>Collate</code> list, but I'm not sure how to indicate this in the roxygen2 documentation format.  </p>
  
  <p>The <a href="http://cran.r-project.org/web/packages/roxygen2/roxygen2.pdf" rel="noreferrer">roxygen2 manual</a> makes some reference to an <code>@include</code> tag but that looks like it might actually just include code in the documentation, for instance, for adding external examples through an <code>@examples</code> flag.  Can this be used for specifying collate order for methods?</p>