There isn't a component that you can use from Flex that will
display a HTML page. The TextArea supports a very small subset of
the HTML standard but that is only like <b> for bold and
<u> for uppercase (and that's about it).
There are workarounds for this that overlay an IFrame from
the hosting browser over the top of the Flex app, and it looks like
the flex app is hosting HTML. The most popular one seems to be this