html_options is a custom function that creates html option group
with provided data. It takes care of which item(s) are selected by
default as well. Required attributes are values and output, unless
you use options instead.
If a given value is an array, it will treat it as an html OPTGROUP,
and display the groups. Recursion is supported with OPTGROUP. All
output is XHTML compatible.
If the optional name attribute is given, the
<select name="groupname"></select> tags will enclose
the option list. Otherwise only the option list is generated.
All parameters that are not in the list above are printed as
name/value-pairs inside the <select>-tag. They are ignored if
the optional name is not given.