📄️ TEI 101
TEI, or the Text Encoding Initiative, is both a set of guidelines for the digital annotation of texts and the consortium that publishes the guidelines. When someone refers to TEI, they quite often are not referencing the body of academics who develop the guidelines, but rather the standards maintained by the TEI Guidelines. TEI is not a markup language itself, but recommendations for the markup of texts in terms of the Extensible Markup Language (XML). For more on XML, see the XML page.
📄️ XML 101
XML stands for Extensible Markup Language, and is a markup language for structured data. In LEAF, you will encounter XML through TEI-XML, a subset of XML which you can learn about here.