Learn in the textbookData Description Languages (Markup Languages and Structured Data Formats)
DefinitionXML is a markup language (マークアップ言語) in which users name their own tags (タグ) to suit their purpose and describe the meaning and structure of data.
ExplanationIts hallmark is that you can create new tags to fit the information at hand; for book data, for example, you might make tags named book, title, author and price and nest them in a hierarchy. Because the tag names reveal what the content means, XML serves as a format for passing data between different systems.
AnalogyIt is like a storage shelf where you can make your own labels. Just as you might put small "family name" and "given name" boxes inside the "author" shelf, you decide how things are divided.
Memory hookThe X in the abbreviation comes from the second letter of eXtensible. The name uses X rather than the initial E.