Notice how the position of the key item changes in the following two "browser windows":

foo foo foo foo foo keyword foo foo foo

foo foo foo foo foo keyword foo foo foo

So to use your example the arrow is attached to the "keyword" but because of formatting the word position changes with window size.
Then perhaps one way would be to combine text and "arrow pointer" into an image and display that in the browser

This is quite clearly best solved by Javascript.

Basically you want to draw your arrow (or whatever) so that its tip points to the area of interest.

Best bet is to:

1. find the area in question (say by using document.getElementById)
2. compute the (possibly relative) position of the element node.
3. reposition/reorient your pointer to point to it.
The second step is generally a difficult problem for arbitrary DHTML documents in various browsers.

I recommend the "walk up the tree" approach... which is basically just walking up the .parent chain from your interesting node until you find the first node that is absolutely positioned.. then you walk back down, asking the browser for the "computed" styles of each container element until you get to the target node, collecting positioning attributes on the way down. You should end up with a "recipe" for how to compute the position of the target-node. (A thorough understanding of DOM, CSSp and browser DOM-bugs is required... implementation left as an exercise for the reader ;)

-David