\textbf{\textit{BoldItalic}} typesets the text in a
bold italic font. Different HTML browsers will display different
things.
The following old-style commands are also supported:
So you can write
{\it italic text}
\textit{italic text}
\/ to separate slanted and non-slanted fonts (it
will be ignored in the HTML-version).
Hyperlatex complains about any other LaTeX commands for font changes,
in accordance with its general philosophy. If you
do believe that, say, \sf should simply be ignored, you can easily
ask for that in the preamble by defining:
\W\newcommand{\sf}{}
Both LaTeX and HTML encourage you to express yourself in terms of logical concepts instead of visual concepts. (Otherwise, you wouldn't be using Hyperlatex but some WYSIWYG editor to create HTML.) In fact, HTML defines tags for logical markup, whose rendering is completely left to the user agent (HTML client).
The Hyperlatex package defines a standard representation for these logical tags in LaTeX--you can easily redefine them if you don't like the standard setting.
The logical font specifications are: