I am not sure about data_specification_iec61360_to_xml() and data_specification_content_to_xml() tho. On the one hand, data_specification_content_to_xml() only has the job to call data_specification_iec61360_to_xml(), resulting in the additional call of data_specification_iec61360_to_xml() in object_to_xml_element() being redundant. On the other hand, data_specification_content_to_xml() wraps the result of data_specification_iec61360_to_xml() into an additional etree._Element. Technically, this is a different result than calling data_specification_iec61360_to_xml() directly. Is this behaviour intended, or can I just delete data_specification_iec61360_to_xml() from object_to_xml_element() ?

I am not sure about data_specification_iec61360_to_xml() and data_specification_content_to_xml() tho. On the one hand, data_specification_content_to_xml() only has the job to call data_specification_iec61360_to_xml(), resulting in the additional call of data_specification_iec61360_to_xml() in object_to_xml_element() being redundant. On the other hand, data_specification_content_to_xml() wraps the result of data_specification_iec61360_to_xml() into an additional etree._Element. Technically, this is a different result than calling data_specification_iec61360_to_xml() directly. Is this behaviour intended, or can I just delete data_specification_iec61360_to_xml() from object_to_xml_element() ?

basyx-python-sdk/sdk/basyx/aas/adapter/xml/xml_serialization.py

Lines 936 to 944 in 6f5e4b8

	elif isinstance(obj, model.DataSpecificationIEC61360):
	return data_specification_iec61360_to_xml(obj)
	# generic serialization using the functions for abstract classes
	elif isinstance(obj, model.DataElement):
	return data_element_to_xml(obj)
	elif isinstance(obj, model.SubmodelElement):
	return submodel_element_to_xml(obj)
	elif isinstance(obj, model.DataSpecificationContent):
	return data_specification_content_to_xml(obj)

Yes, I fully agree with you that this is ugly, but sadly it is intended.
The reason for this weird construct is that in theory people can add arbitrary data to the AAS via a DataSpecification. However, obviously no one can actually parse arbitrary data, so in practice there's only one DataSpecification, that is DataSpecificationIEC61360 actually defined in Part 3a of the specification. So in order to be compliant with the specification, we do need this extra wrapped XML element.

Furthermore, our extra function exists in order to future proofs our implementation a little bit (e.g. when Part 3b with a new DataSpecification gets released).