What form of code was developed in 1990 specifically for creating websites?

Hypertext Markup Language (HTML) was developed in 1990 and is specifically designed for creating and structuring content on the web. It provides a standardized way to present text, images, links, and other elements on web pages, enabling browsers to render this content for users. HTML defines the structure of web documents using a series of elements and tags, which dictate how content is displayed and organized on the page.

While Cascading Style Sheets (CSS) is used to control the presentation of HTML elements, it was not developed as a foundational coding language for websites. JavaScript, introduced shortly after HTML, is a programming language that adds interactivity to web pages, but HTML remains the primary language for webpage structure. Extensible Markup Language (XML) serves different purposes, primarily for data storage and transport rather than directly creating websites. Thus, HTML is the essential and correct answer for website creation from that timeframe.