where do I learn how to write a html parser?

[unregistered]

as above...
don't intend to use libraries as I want to know how it works.

[guestgulkan]

I would say - Start with a book on the HTML standard.

[Bazzy]

The HTML specifications are publicly available
http://www.w3.org/TR/1999/REC-html401-19991224/

[webJose]

Remember that there is HTML and there is XHTML and who knows what will come in the future. And also remember that there have been several versions of HTML so you want to make your parser aware of these important notes so it doesn't break easily across versions of HTML.

[PanGalactic]

The easiest way depends on how you best learn. For me it would be to dissect an existing HTML parser. There are lots of open source libraries and programs to learn from.