OK, so, at this stage the main thing this blog is for is to find out how to import existing blog posts into Blogger. Brief summary: my existing blog uses a blogging engine I wrote myself back in 2000; it's quite a good blogging engine but it's not used by very many people because I didn't promote it enough back in the day, and so it's time to end-of-life it and migrate the existing users to something else.
Blogger has a mechanism for exporting and importing blogs. So, I thought, it ought to be possible to generate the export format, which is documented here, from my existing data and then import that. From the documentation it was clear that the format was slightly bizarre - a well formed XML wrapper around data which is actually XML and presumably also well formed but is represented as text. However, I generated stuff that looked right to me according to the documentation, and it failed to import.
Worse, the error message given was terse to the point of unusability, and there's apparently no documentation of the error codes available on the web.
So the next thing to do was to export this blog from Blogger, and see whether the export file format looked anything like the documentation. And, guess what, it sort of doesn't. Which is to say that while the file format shown in the documentation is a very small subset of what's actually generated, it is such a noddy example that it doesn't even nearly represent what one needs to generate.
And, of course, there's no guarantee that even if I did succeeded in generating all the cruft that's in the format as generated by Blogger, I'd get my data to reimport - since the format includes magic identifiers which may represent objects in Google's persistent data space.
So it may be time to think of other ways to work around this.