I have a web site with a large number of hand coded pages. I have a block of code that needs to be inserted into each page. The problem is that the block will change occasionally as new material is added. Obviously, things would be much simpler if I could make the change in one place and have each page attach/include/link to/etc. a file containing that piece of code. If there is an HTML construct that allows that, I haven't found it.

If there is such a thing and someone could point me to it, It would be greatly  appreciated.

Mark Jarvis