def edge_type_to_class(edge_type):
    """Return the edge class for layout purposes based on the edge type"""
    edge_type = edge_type.lower()
    if 'amount' in edge_type:
        return 'amount'
    if edge_type in ('activation', 'inhibition'):
        return 'activity'
    if edge_type == 'complex':
        return 'complex'
    else:
        return 'modification'