20. the main goal of extensible hypertext markup language (xhtml) is to
XHTML XHTML was developed to make HTML more extensible and increase interoperability with other data formats.[8] In addition, browsers were forgiving of errors in HTML, and most websites were displayed despite technical errors in the markup; XHTML introduced stricter error handling.[9] HTML 4 was ostensibly an application of Standard Generalized Markup Language (SGML); however the specification for SGML was complex, and neither web browsers nor the HTML 4 Recommendation were fully conformant to it.[10] The XML standard, approved in 1998, provided a simpler data format closer in simplicity to HTML 4.[11] By shifting to an XML format, it was hoped HTML would become compatible with common XML tools;[12] servers and proxies would be able to transform content, as necessary, for constrained devices such as mobile phones.[13] By using namespaces, XHTML documents could provide extensibility by including fragments from other XML-based languages such as Scalable Vector Graphics and MathML.[14] Finally, the renewed work would provide an opportunity to divide HTML into reusable components (XHTML Modularization) and clean up untidy parts of the language.[15]
Hypertext In 1945, Vannevar Bush wrote an article in The Atlantic Monthly called "As We May Think", about a futuristic proto-hypertext device he called a Memex. A Memex would hypothetically store - and record - content on reels of microfilm, using electric photocells to read coded symbols recorded next to individual microfilm frames while the reels spun at high speed, stopping on command. The coded symbols would enable the Memex to index, search, and link content to create and follow associative trails. Because the Memex was never implemented and could only link content in a relatively crude fashion — by creating chains of entire microfilm frames — the Memex is now regarded only as a proto-hypertext device, but it is fundamental to the history of hypertext because it directly inspired the invention of hypertext by Ted Nelson and Douglas Engelbart.