Need more information about custom attributes creation in client

[dmrlx]

For example I want to locate all managed objects, which have next attributes (including custom):

'Type': 'Symmetric key'
'State': 'Active'
'x-DriveID': 'Samsung_12345'

For first two attributes I can do next:

f = attributes.AttributeFactory()
attrs = [f.create_attribute(enums.AttributeType.OBJECT_TYPE, enums.ObjectType.SYMMETRIC_KEY)]
attrs.append(f.create_attribute(enums.AttributeType.STATE, enums.State.ACTIVE))

But I can't understand how to create custom attribute 'x-DriveID' with 'Samsung_12345'

Could you please give some info. Also I think it will be fine to add such information to documentation.