- XML (eXtensible Markup Language) is becoming the de-facto standard for data description. Data presentation is not in its scope.
Like HTML, it structures data with tags. For example <title>...</title>.
Unlike HTML, these tags are user-defined.
Unlike HTML, the document must be well-formed (opening tags must be matched by closing tags).
Besides, for some applications, the documents must also be valid (only some tags and values are allowed). This validity is described in a DTD (Document Type Definition).
- HTML (HyperText Markup Language) is a data presentation language. This is the language of the World Wide Web.