Concepts
XML and Markdown
Understand XML syntax, XML-like elements, and their portability in Markdown.
XML is a separate markup language with strict rules for well-formed documents, element nesting, attributes, namespaces, and self-closing elements.
Markdown does not define universal XML processing. Many Markdown parsers will preserve XML-like tags as raw inline markup, but the resulting interpretation depends on the Markdown flavor and renderer. Syntax that is well-formed XML is not automatically meaningful HTML, and valid HTML is not always well-formed XML.
Portable extensions such as the proposed <fm-var> must
define how their syntax behaves in Markdown source, Markdown syntax trees,
HTML, XML-aware tools, and contexts that do not recognize the element.