this is a customisation/extension of HTML on apples part and will only work on safari within tiger.
apple seem to have no ADC docs on it so i dont know any more about any variables except for what ive scavenged (maily from apples dashboard widgets site) but what i do know:
<input type="search" name="q" placeholder="Search Dashboard Widgets" autosave="Apple Downloads" results="5" class="sbox" id="q">
Placeholder = the text in grey before you type
Autosave = you have to specify the name for a cookie to enable the little drop down search history - site name usually does
Results = number of previous searches displayed by clicking the droppy arrow 0 disables search history
dont quite know what the rest do
hope this helps