This identifies the DTD that will be used in the document and which will be the element root, in this case article . Every article begins with a header, where there are the title, author and the several revisions of the same article. This is the classic definition of header for an article. Now I will present pair of essential notes. The first is that every article must have a definition for the header.
Every section needs a title.
Our title is First Para. We've learned to install and to make a short document. I've afraid to duplicate already existing documentation.