As laid out in more-or-less vague terms, we've had some pretty interesting plans here. I'd like to detail a bit about what's going on, what's in and what's not with this feature.
A cross reference is a reference to a place in a document (or anywhere, for that matter). To be sure, anyone can refer to anything by simply typing "see page 12" (if one wishes to refer to something on page 12), but a cross reference allows you to refer to a point in the text and have that reference change dynamically when that point changes position (e.g., when it is no longer on page 12 but on page 13, 14 or 112).
Mellel 2.5 will allow you to refer to three types of things:
A. A bookmark -- a place holder or a bookmark you've set in the text (by choosing Insert > Cross Reference > Bookmark).
B. An element in the text -- auto-titles, for example, can be referred to. For example, in the image below, the reference (see "Lorem Ipsum") refers to the auto-title.
C. An abstract reference to a "virtual target" that may not even exist in the text. For example, a reference to a part of the document that have not been written yet.
The key to a good cross-referencing system is efficient referencing. To enable that, when you enter a reference, you can view all the bookmarks you've entered, and all the potential targets (e.g., all auto-titles may be targets for reference).
To enter a reference, all you need to do is click on one (either an existing one or a potential one) in the list in the Reference entry dialogue (You'll see it "in context" of the text it's in, to make selection easy) and click OK and you'll have a reference to the page number of the selected target.
But, of course, most of you would like to do more than that. For example, sometimes you wish to refer to the text of an auto-title (as seen above), or to a page range of the auto-title (as in referring to a whole chapter), or you may want to refer to a footnote number, and so on. That is possible too, of course.
But, of course, that's not all. You may also want to take the reference to a higher level and refer not just to the place the bookmark is, but also refer to it in relative terms. The bookmark may be above or below the reference, on the page before or after, on the opposite page, etc. You can do that too.
Finally, it would be rather tedious entering all those elements over and over again. That may not be a problem if you only wish to have "see page XX" type of references, but if you wish to have "See pages XX-YY (chapter "ZZZZ")" type of references, that may turn out to be quite a handful. To avoid that, you can simply save the reference format for posterity (or the next time around) and re-use it anytime you want.
There's more, of course. You can, for example, control the way the reference appears in the text, having it appear using a different style than the rest of the text, tying of virtual targets to a real place in text (once you're written the chapter), and more.
Hope this serves as a general survey of this feature.
