I'm maintaining a corporate website of several dozen pages. Currently, if I update the main menu, I have to change it on every page. I'd like to set up a global menu as a single document accessed by each of the pages. What are my options?

I'd like to stick to html5/css3 and avoid frames.

Our systems engineer suggests this approach: calling out a single javascript file from each html document and then embedding the menu's html and css into that javascript file. He's seen html embedded that way, and thinks it ought to be possible to include css as well.

Any thoughts?

With any solution, what are the SEO implications?