Unfortunately, there are
things that HTML just can't do for you.
Fortunately, HTML is growing
quickly to meet these needs.
no matter how many new tags are added, there
will never be enough for all the good ideas people keep having.
Fortunately, HTML is a form of SGML
Markup Language), an ISO standard that allows you to invent the tags you
need, and declare them so others can use them.
Unfortunately, the SGML standard is large,
takes time to learn, and doesn't have a "starter kit".
Fortunately, XML is here.