Bookcase uses XSL Transforms for printing, importing, and exporting. My XSLT files are very, very messy. I just bought XSLT Cookbook by Sal Mangano, so I have hopes of cleaning them up, but I thought I might put them up on the website in case anyone wants to look them over without downloading the whole package.
They are listed on the left-hand sidebar. bookcase-printing.xsl is used for printing, and has several parameters passed in for formatting options. The files starting with bookcase2 transform Bookcase documents into other formats, and bibtexml2bookcase.xsl is a rough cut for transforming Bibtexml into Bookcase format. I included two other files just for general information, which sort by author and title.