On a few pages in the YUI documentation there's mention of an
<input type="textbox" ...> which simply doesn't exist in HTML. My guess is that
<input type="text" ...> is what was meant.
Pages that have this error include the following
HTML 4.01 Specification, Section 17.4 - The INPUT element [http://www.w3.org/TR/html401/interact/forms.html#adef-type-INPUT]