Leaving dangling cross references when writing a book is like leaving dangling hyperlinks in a Wiki—they’re both a promise and a question.
I’m deep down in the bowels of writing the new Rails book. As usual, I’m adopting a fairly agile development style, moving stuff around between chapters, adding and deleting whole chapters, and generally working stuff out as I go along.
One of the tricks that I discovered myself using is the dangling cross reference. If I’m writing some introductory material, for instance, I might do something such as
Of course, you'll need to tidy those session files. We'll talk about this later in <pref linkend="sec.tidy.session.files"/>.
(Our books use a simple XML markup, and <pref…> creates a cross reference [including a page number] to a named tag.)
As I haven’t yet written about tidying session files, when I format the book, the cross reference shows up as
about this later in ? on page ?.
But even better, the formatting process itself summarizes the list of all missing cross references.
This all means that as I write, I can drop in these references, not caring if the section exists. Every now and then I’ll look through the list of unknown tag names. If I’ve since written about that material, I’ll marry the text and the tag. If I haven’t I’ll know that at some point I’ll have to add more text on the subject.
In a WikiWiki web, a CamelCase word referencing an unwritten page acts as a promise of future content, and as an invitation for someone to produce that content. The same seems to apply to writing books. It’s fascinating to see the list of unfulfilled tags ebb and flow as the Rails book progresses. It’s a kind of dialectic writing process.