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59. combineCss(): Combine CSS classes from different sources

The purpose of this function is to assist in building an XHTML element that may have class attributes attached that come from multiple sources. It accepts a variable number of arguments, each of which specifies zero or more CSS class names in the form described in Section 14.2, “class-dict.

For example, et.CLASS('a', 'b') would return the dictionary {'class': 'a b'}. The manifest constants defined in Section 13.4, “CSS constants”, which have names starting with “CSS_”, specify CSS classes in this way.

The purpose of the combineCss() function, then, is to produce a class-dict dictionary that combines class names from multiple sources. The function takes a variable number of arguments, each of which can be either None or a class-dict. If none of the arguments specify any class names, it returns an empty dictionary, otherwise it returns a class-dict that includes all the specified class names.
# - - -   c o m b i n e C s s

def combineCss(*cssList):
    '''Build a class-dict from multiple class-dicts.

      [ cssList is a list whose members are either class-dicts
        or None ->
          if cssList is empty or contains only None elements ->
            return a new, empty dictionary
          else ->
            return a class-dict representing all the class names
            named in cssList ]
    #-- 1
    nameList = []

    #-- 2
    # [ nameList  +:=  classes named in cssList ]
    for d in cssList:
        #-- 2 body
        # [ if d is None ->
        #     I
        #   else ->
        #     nameList  +:=  classes named in d ]
        if d is not None:
            nameList += d['class'].split()

    #-- 3
    if len(nameList) == 0:
        return {}
        return {'class': ' '.join(nameList)}