Domino generates the code (so you don't need to) but it's limited to a 3 doc types:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
NOTE: Setting the doc type does not change the code domino generates, just the doc type in the header.
To get XHTML:
If you don't need to access domino data, then file resources can be used with webdav, pages or forms set to content type html.
To access Domino, pages with computedtext for the data access can be used.
To save data to domino, you'll have to create agents or create a notes form to accept the data.
The other choice is to use apache and odbc to access the domino server. Like learning Eclipse, Domino has it's own set of rules to follow.