IFAC and other accounting organizations are discussing the topic to decide on a common approach and XBRL auditing standards.
The auditor performs an audit on every layer of the digital reporting supply chain, with assistance of experts and use of software tools on specific areas.
In order for the auditor to be able to give the assurance, several aspects need to be clear: With XBRL assurance the auditor needs to distinguish between primary and secondary audit objects: The term standard taxonomy is here used in the context of clear ownership.
The auditor needs to validate the custom (extension) taxonomy, a secondary audit object.
He needs to perform an audit to check if this taxonomy complies with regulations and if it is accurate and complete.
Material misstatement concerns the accuracy of the audit opinion on a financial statement or filing as a whole.
Material misstatement in an XBRL report concerns the individually identifiable business facts.
The split in primary and secondary audit objects with different audit reports (and opinions) is necessary to prevent any confusion about the assurance the auditor adds to the XBRL financial statement instance or any other XBRL report without presentation in a human readable form.
Both the primary and the secondary audit objects are electronic files which can be altered without leaving a trace.
These business rules can be found in different places in the XBRL taxonomy, that is in datatypes or linkbases.