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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def removeUnreferencedIDs(referencedIDs, identifiedElements):
 """ Removes the unreferenced ID attributes. Returns the number of ID attributes removed """

    global _num_ids_removed
    keepTags = ['font']
    num = 0
    for id in identifiedElements:
        node = identifiedElements[id]
        if id not in referencedIDs and node.nodeName not in keepTags:
            node.removeAttribute('id')
            _num_ids_removed += 1
            num += 1
    return num