Answering the Question: What the hell is xml?

Mike Shatzkin writing in Publisher's Weekly answers the question in the headline:

First: recognize reality. For many titles, you aren't going to sell as many copies as you used to, and your standard marketing practices of the past few decades won't be nearly as cost-effective.

Second: come up with a strategy to suit the new reality. There are many conceivable ones, and they depend largely on what you publish, but two things are certain: you are going to want more direct contact with end users than you had before and you are going to find users congregating at Web coordinates that appeal to subject interests (or niches).

Third: recognize that your content is now “unbound.” You can still sell it in “book” format, but you will also be selling it in smaller units (chunks) or in larger units (books put together as databases) as well. And you will certainly be using chapters, excerpts, TOCs and other parts of your book in marketing, if you aren't already.

And that's where XML comes in.

XML stands for “extensible markup language” (and no fair asking why it isn't “EML”). XML uses tags to associate any information you want with any part of a document (i.e., a book). That is, your document file in XML resembles a database, with a structure you define to track elements of the document. It contains not only the printable text and information about the art (though not the art itself), but it can also contain any piece of useful information about the document or about any piece of it.

Publisher's Weekly.