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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 create_class_instance(element, element_id, doc_id):
 """ given an Salt XML element, returns a corresponding `SaltElement` class instance, i.e. a SaltXML `SToken` node will be converted into a `TokenNode`. Parameters element : lxml.etree._Element an `etree._Element` is the XML representation of a Salt element, e.g. a single 'nodes' or 'edges' element element_id : int the index of element (used to connect edges to nodes) doc_id : str the ID of the SaltXML document Returns ------- salt_element : SaltElement an instance of a `SaltElement` subclass instance, e.g. a `TokenNode`, `TextualRelation` or `SaltLayer` """

    xsi_type = get_xsi_type(element)
    element_class = XSI_TYPE_CLASSES[xsi_type]
    return element_class.from_etree(element)