Very interesting post by Tim Berners-Lee, the inventor of the Web.
Some things are clearer with hindsight of several years. It is necessary to evolve HTML incrementally. The attempt to get the world to switch to XML, including quotes around attribute values and slashes in empty tags and namespaces all at once didn’t work. The large HTML-generating public did not move, largely because the browsers didn’t complain. Some large communities did shift and are enjoying the fruits of well-formed systems, but not all. It is important to maintain HTML incrementally, as well as continuing a transition to well-formed world, and developing more power in that world.
I say this as one of the few people in the world who spent a year building an XHTML/XML web site: it ain’t worth it. As long as XHTML is the end product, and as long as browsers don’t care too much what you feed them, then XHTML does not and will not matter.
I always assumed that XHTML would find applications as a data source, but alas, it is not and will never be a good data source. I will keep on producing valid XHTML code whenever convenient, because working with XHTML is just better than working with tag soup, but there other formats, such as HTML 4.0, which are better than tag soup.