Learn in the textbookData Description Languages (Markup Languages and Structured Data Formats)
DefinitionSGML is an international-standard metalanguage (メタ言語) used to define the markup languages themselves, which structure documents with tags.
ExplanationA metalanguage is a language for setting the rules of how another language is written. SGML is a standard that predates HTML and XML, and both were built on it. On today's web, SGML is almost never written directly.
AnalogyIt is like a "guide to designing formats" that exists before any individual format is designed. Formats for each purpose branch off from that guide.
Memory hookStandard Generalized = standard and general-purpose. The name carries the idea of a root standard that comes before narrowing to any particular use.