'Return a new ``<w:num>`` element having numId of *num_id* and having
a ``<w:abstractNumId>`` child with val attribute set to
*abstractNum_id*.'

@classmethod
def new(cls, num_id, abstractNum_id):

    num = OxmlElement('w:num')
    num.numId = num_id
    abstractNumId = CT_DecimalNumber.new('w:abstractNumId', abstractNum_id)
    num.append(abstractNumId)
    return num
