How do you compare two images for similarity? One way is by hashing them using something like JImageHash. Libraries such as this reduce an image to a much smaller binary hash. The idea is that when hashing two images which look similar (but aren’t identical), the two hashes will be very similar. It’s possible then to get a ‘similarity score’ by finding how many bits in the two binary hashes are different.
The XHTML 1.0 specification is basically an attempt by W3C to provide a new standard of http markup, with much greater compatibility over various ‘user agents’, without breaking anything.
The Web Developers' Virtual Library says it well:
Portability: By the year 2002 as much as 75% of Internet access could be carried out on non-PC platforms such as palm computers, televisions, fridges, automobiles, telephones, etc. In most cases these devices will not have the computing power of a desktop computer, and will not be designed to accommodate ill-formed HTML as do current browsers (bloated with code to handle sloppy or proprietary HTML).