Working on Internet Explorer extensions in C++ & COM, I had to relearn or rediscover how to do several totally basic and important things. To save myself and possibly others trouble in the future, here's some pertinent links and tips.
First you must choose your IE extensibility point. Here's a very short list of the few I've used:
Once you've created your COM object that implements IObjectWithSite and whatever other interfaces your extensibility point requires as described in the above links you'll see your SetSite method get called by IE. You might want to know how to get the top level browser object from the IUnknown site object passed in via that method.
After that you may also want to listen for some events from the browser. To do this you'll need to:
If you want to check if an IHTMLElement is not visible on screen due how the page is scrolled, try comparing the Body or Document Element's client height and width, which appears to be the dimensions of the visible document area, to the element's bounding client rect which appears to be its position relative to the upper left corner of the visible document area. I've found this to be working for me so far, but I'm not positive that frames, iframes, zooming, editable document areas, etc won't mess this up.
Be sure to use pointers you get from the IWebBrowser/IHTMLDocument/etc. only on the thread on which you obtained the pointer or correctly marshal the pointers to other threads to avoid weird crashes and hangs.
Check out Eric's IE blog post on IE extensibility which has some great links on this topic as well.
If you view a plain text document in Internet Explorer 8, for instance the plain text version of Cory Doctorow's book Little Brother and press F12 to bring up the developer toolbar, you can see that IE simply takes the plain text, sticks it inside a
tag, and renders it. This means that word wrapping isn't supplied and the only line breaks that appear are those in the document. However, since the text document is converted to HTML it means I can implement word wrap myself using a bookmarklet:
After adding a favorite and setting the favorite's URL to the previous, I can view plain text documents, and select my Word Wrap favorite to apply word wrap and non-fixed width font.