def urlargs_replace_text_in_arg(urlargs, regexp_argname, text_old, text_new):
    """Analyze `urlargs' (URL CGI GET query arguments in string form)
       and for each occurrence of argument matching `regexp_argname'
       replace every substring `text_old' by `text_new'.  Return the
       resulting new URL.

       Used to be used for search engine's create_nearest_terms_box,
       now it is not used there anymore.  It is left here in case it
       will become possibly useful later.
    """
    out = ""
    # parse URL arguments into a dictionary:
    urlargsdict = parse_qs(urlargs)
    # construct new URL arguments:
    urlargsdictnew = {}
    for key in urlargsdict.keys():
        if re.match(regexp_argname, key):  # replace `arg' by new values
            urlargsdictnew[key] = []
            for parg in urlargsdict[key]:
                urlargsdictnew[key].append(parg.replace(text_old, text_new))
        else:  # keep old values
            urlargsdictnew[key] = urlargsdict[key]
    # build new URL for this word:
    for key in urlargsdictnew.keys():
        for val in urlargsdictnew[key]:
            out += "&amp;" + key + "=" + quote_plus(val, '')
    if out.startswith("&amp;"):
        out = out[5:]
    return out