From the w3schools:
The id attribute specifies a unique id
for an HTML element.
The id must be unique within the HTML
document.
The id attribute can be used by a
JavaScript (via the HTML DOM) or by
CSS to make changes or style the
element with the specified id.
and
The class attribute specifies a
classname for an element.
The class attribute is mostly used to
point to a class in a style sheet.
However, it can also be used by a
JavaScript (via the HTML DOM) to make
changes to HTML elements with a
specified class.
The class attribute cannot be used in
the following HTML elements: base,
head, html, meta, param, script,
style, and title.
It is possible to assign multiple
classes to one HTML element, e.g.
.
This allows you to combine several CSS
classes for one HTML element.
