include in html

Hello there,

I don't understand why there's no instruction to include a file
in html in another. For example, I have a menu.html file which
describes the main menu, and for all *.html in the site, I would
include the menu simply by putting something like :
 <INCLUDE HREF="menu.html">  
(like the \insert{} command in LaTeX or the #include in C langage)
I think that this can be useful in many cases.
(I know that it's possible to do frame pages but I don't want)

Thank you for respond,
Pascal Sitbon
ps@chez.com