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Back in the dimly remembered, early years of the Web (1990–1993), HTML was a fairly lean language. It was composed almost entirely of structural elements that were useful for describing things like paragraphs, hyperlinks, lists, and headings. It had nothing even remotely approaching tables, frames, or the complex markup we assume is necessary to create web pages. HTML was originally intended to be a structural markup language, used to describe the various parts of a document; very little was said about how those parts should be displayed. The language wasn't concerned with appearance—it was just a clean little markup scheme.
Then came Mosaic.