NetMechanic and Javascript
This link shows a convenient method for including headers and footers on web pages. A footer might present, for example, copyright information to be used on all pages at your web site. NetMechanic gives a link to a sample page showing a header and a footer.

W3C and Javascript
Using Javascript in your HTML source code can lead to conflicts with W3C HTML standards. With a few changes, a script for the display of the current date gives "happy results" from an SGML parser.