[whatwg] [WF2] Why does list="" work with <select>?

[Simon Pieters]

WF2 says:

    When a control has a list attribute, it specifies an element from which
    to derive the list of author-specified autocompletion values for the
    control.

    The element specified is the one that would be returned when calling
    getElementById() with the value of the list attribute as the argument,
    if the returned value is an element node with either the local name
    datalist or the local name select, and (for XHTML) with the XHTML
    namespace. If the attribute is present but either specifies an ID that
    is not in the document, or specifies an element that is not an (X)HTML
    datalist or select, then it must be ignored.

      -- http://www.whatwg.org/specs/web-forms/current-work/#the-datalist

Why does it work together with <select>? What are the use-cases for having  
a combo box where the select is also visible? It doesn't make any sense to  
me.

-- 
Simon Pieters