Markup schemes are standards which have been developed to make markup easier to do. Instead of going through the effort of devising your own markup and DTD or XML Schema for a project you can use an off-the-peg scheme instead. This should contain a fully worked-out markup system and, of course, the DTD or XML Schema that validates that markup.

Some advantages to using an established markup scheme are

• The texts created with it will be interoperable with the body of other texts also using that markup scheme
• It is likely to be pretty comprehensive: most problems will already have been encountered (and solved) by others
• There is a likely to be a user community associated with the scheme, which will allow you to ask technical questions, get advice on how to mark up a particular piece of a text, or even suggest changes to the scheme 

There are many such markup schemes, and your choice will depend on the base text that you want to mark up. Here we are going to concentrate on the Text Encoding Initiative (TEI), which is widely used and well suited to running text. At the end of this module we’ll touch on a few other options, in case you want to explore them instead.