The WebClass "listbox" is used to display a list of values with the
<select> tag of HTML. These values are taken from a recordset (which
can be retrieved from DB or can be supplied by PHP code. The recodset 
associated with the listbox must have two fields: 'id' and 'label'.
'label' is the field displayed, and 'id' is the value that is selected,
saved in DB and retrieved from DB.

Recordset example:
  <Recordset ID="listbox::country">
    <Query>
      SELECT country_id AS id, country_name AS label
      FROM countries
    </Query>
  </Recordset>

Usage example:
  <Include SRC="{{LISTBOX_PATH}}listbox.html" />
  <WebObject Class="listbox" Name="country" 
             value    = "selected_value"
             rs       = "rs_id"
             onchange = "alert(this.options[this.selectedIndex].text)"
             width    = "---------------" />

The attribute "value" is optional. It has the value of the selected item
(the item with id equal to this value is the one that will be selected).
It can be a variable, like this: value="{{var_name}}", in this case the
value of this variable is used.  If it is not given, then its default
value is '{{{{obj_name}}}}' (in the example above, it would be '{{country}}',
since the name of the object is 'country'; this means that the value of
the variable {{country}} will determine which item will be displayed as
selected).

The attribute "rs" is optional. Its default value (if not specified) is
{{obj_id}} (in the example above, it would be 'listbox::country').

The attribute "onchange" (all lowercase), is optional and is used as 
the "onchange" attribute of the <select> tag.

The attribute "width" is also optional; it is used as the last line of the
list, in order to keep the width of the <select> to a certain size, and
can also be used as a "nothing selected" (none of the above) value.

This WebClass uses a <select> tag like this:
        <select name="{{obj_name}}" id="{{obj_name}}" onchange="{{onchange}}">
          . . . . .
        </select>
So, this should be kept in mind when accessing the selected value
and when giving an initial value.
If the 'listbox' is used inside a 'formWebObj' webbox, then it 
takes care of it automatically.