Re Usable code and HTML pages

Adobe GoLive calls them GoLive components that the user creates and saves as an
external HTML file that then gets inserted into the current working file.

For instance... if we have multiple pages that Use a Navigation and the
navigation changes every so often, You can make a Nav.html that is called by
each page so when the nav changes, all you need to do is change the one file
and all the pages that use it are automatically updated... Isn't this possible..

Lee