XML stands for Extensible Markup Language. The idea is to “separate concerns”, i.e separate the presentation of a text from its structure. So if a text has an author, a title and a body, these three things would be tagged as such. And if the text were printed, or published as an ebook, a stylesheet would determine how that title would look on paper or on the screen.
The XML tags surround the content they tag. So there is always an opening and a closing tag:
<author>Kate</author>
<title>Peanut butter</title>
<body>Peanut butter is nice and healthy.</body>
There is one exception: when a tag has no concents, the opening and closing tag may be combined: <author/>.
<author> is an element. It can have an attribute, for example <author dateofbirth="20020202">. In this case dateofbirth is an attribute, and 20020202 is its value.
An XML file has an .xml extension and always starts with the XML declaration to tell the computer it is XML: <?xml version="1.0" encoding="UTF-8"?>
A tag always has pointy brackets and there must always be an opening and end tag.
Also, tags may be nested - sit inside each other, like <author><firstname>Kate</firstname></author> but can never overlap (like <author><firstname>Kate</author></firstname>)
If any of these things is wrong, the XML file is not “well-formed” and your computer will be unhappy.
Tags can be anything you want. In any language, in any script. This also means that nobody knows what they mean - except you. Even for a seemingly obvious tag like <author>, you don’t know how it is used unless someone tells you. You can write down how you use the tags. This is called a schema. A schema tells the computer what tags you use, and how they may be combined.
For example, you may say: in my world, the author tag always has two children, first name and last name. They may not be empty, and there must always be the two of them.
Some XML files contain a pointer to the schema, so the computer understands what the rules are. That may look something like this <!DOCTYPE encyclopedia SYSTEM "Encyclopedia.dtd">.
If your XML file conforms to these rules, it is valid. If not, your computer will be unhappy.
At Brill, the BrillOnline Reference Works “platform” expects XML files to be one of two schemas:
Make sure to follow the XML Tutorial at W3 Schools. It is short, clear, and you can tinker online without breaking anything.
XML is plain text and so any text editor may be used to create or edit XML files. Many have plugins that allow you to style your XML and to validate it.
There also exist dedicated XML editors (sometimes called “parsers”). Scholars tend to use Oxygen, which is very powerful but costly. Numerous open and free alternatives exist.
At Brill, we have a limited number of licences for Oxygen-. In the remote, we have _XML Copy Editor that anyone can use.