[xsl] Integrated sort using different elements

[Quinn Dombrowski <qdombrow@xxxxxxxx>]

Hello,

I'm trying to figure out a way to sort by one of multiple elements, with 
descending priority. I'm working with a TEI bibliography, and there's no 
single element that all the entries have. Ideally, I'd like to sort by 
monogr/author; but when that's not possible, by analytic/author; if not 
that, monogr/editor; then monogr/title; and so on down the line.

Doing a series of sorts, one after another, doesn't work because it 
groups together all the entries with a monogr/author, then all the ones 
with an analytic/author. I need all the entries integrated together into 
one single A-Z list-- where the entry's place is determined by the first 
of the above elements that it has. I can't do "monogr/author | 
analytic/author" because some entries have both.

Here's what a complete (for this purpose) entry looks like-- most 
entries are missing one or many of these elements:
       <biblStruct>
         <analytic>
           <author>Author Name</author>
           <title>Article Name</title>
         </analytic>
         <monogr>
   <author>Other Author Name</author>
           <title>Journal Title</title>
   <editor>Editor Name</editor>
         </monogr>
       </biblStruct>

Any help would be wonderful. Thanks!

~Quinn