[NTG-context] Struggling with xml/epub export (where did the cow go?)

I am still trying to get export-example.tex from the distribution to export to xml/html/epub. Thanks to all the help I got, I have the directory trees export-example-export and export-example-epub. The file export-example-div.html renders nicely in a web browser, except for the missing figures. I added mill and hacker to the images directory and got them to render, but the conversion of cow.pdf to svg I did not manage. Instead, when I run the epub conversion, the cow just disappears from the directory. This is obviously only the beginning of my problems. Where do I learn the basics of XML so that I can style the (say) the headers, theorems, exercises etc? Thanks for any hints! Matthias