XHTML was created but XML codes can be sloppy, like a code can either be all caps or not and not closing the tag properly, the outcome stays the same. (1 jan 1999 ano – 1 jan 2002 ano)
Descrição:
 https://blog.rackspace.com/internet-history-html-evolution 
Adicionado na linha do tempo:
Data:
1 jan 1999 ano
1 jan 2002 ano
 ~ 3 years