First introduced in 1996, XML has gathered a huge momentum as the open data sharing language for the Internet. The core functionality of the language is to structure data. To begin with, XML looks very much like HTML. The language is tag based. There are some exceptions. XML itself is not a presentation language. That is, what you see is just the data. You need to leverage technologies such as Cascading Style Sheets to format the data.
A lot of client ask me to add a "simple" ContentManagmentSystem to their site so they can moderate and update everything themselfs, all good. There are some cms's freely available on the web and they work just fine. (like Textpattern but you might not be jumping around waiting for to learn php and sequel just yet)
Even more clients ask me, what's the difference between blogs now and sites before, do you think I need a blog or a site, and if I use a cmsystem then what's the difference between a blog and and a 'normal' website. Too much to swallow for one bite but XML covers a great share of understanding these questionmarks.
XML allows us to easily load external data into the static layout (often referred to as 'a container') that data can be steared and archived by external applications which allows a handy 'update' or blogpost.
A blog is in fact nothing more than an empty oldskool static website where-in the content is loaded, mostly via XML. So a website updated though a cms basically is a blog. But a blog or better yet blogging itself is overally the description of a concept. Not just providing information but logging information, thaughts and all kinds of data on a regular base and publishing it, more often than not, globally, on the web.
There's a lot more to say on this topic but heck, I just wanted to bring a small "ode" to the creators of XML. Thanks guys, for making our lives easier and my work more complex! :)