Document annotation involves liberally sprinkling throughout a document comments that help clarify the meaning of the code contained in the document. In HTML, this can be done using the syntax between the following quotes: "<!-- comment text-->". For example, if a user wanted to add the comment "The previous line points to a location on the Web that defines document annotation" to an HTML document, it might look like this:
<!--The previous line points to a location on the Web that defines document annotation.-->
Do not use any special characters embedded in the comment field as unexpected results can occur. Most browsers today will interpret the document annotation syntax above correctly.
It is generally considered good programming etiquette to document programs and Web pages. Aside from being a great learning tool for those that follow in your footsteps, it's also a great memory jog for your own sake when viewing pages long after you've written them.