HTML, its problems and the proposed solutions

Invalid HTML: applications produce invalid HTML or introduce vendor-specific extensions; browsers do not reject invalid HTML.
Broken links: problem of deleted or moved Web pages (use URN).
Fixed grammar: HTML is a fixed SGML DTD (language syntax); no standard way to extend, adapt, renew the language.
Limited support for meta-data: what about keywords, search-engines, re-use of the same source file.
Absence of structural tags: HTML tags control mainly appearance not structure; navigation difficult.
Data exchange difficulties: HTML aimed at presentation (Latin1 codes); difficult for data mining, internationalisation, exchange.
Absence of modern features: Web changes rapidly; HTML must adapt smoothly to new technology (dynamic clients with applets, object data model, etc.).

Extend HTML: HTML 4/4.1 W3C Recommendations.
Cascading Style Sheets: CSS1/CSS2 recommendations to decouple presentation from content.
Dynamic HTML (DHTML): provides functionality to add dynamic representation to Web pages.
Document Object Model (DOM): allows programs to access HTML (XML) elements as a structured collection of object data, each having a set of properties and methods.
Extensible Markup Language (XML): offers better application-specificity and better data organisation.
XHTML: a redefinition (and modularisation) of HTML 4.x as a series of XML DTDs.

A problem is that at present very few browsers, if any, support these new features