Hiding information in ESEF files
Every iXBRL/ESEF file has a hidden section, which is usually referred to as the “ix:hidden section” and although a name like “the hidden section” does make it sound like the perfect place to hide anything you don’t want the public to see, that is not the case.
A way to ensure that you don’t have anything illegal in the hidden section, is to upload your finished ESEF file to an ESEF validation tool, such as the ParsePort XBRL Inspector.
What Is the ix:hidden section in an ESEF file?
The purpose of the hidden section is to have a place to store content which is not intended for display. Now, this may very well sound like the perfect place for Al Capone to store his secrets, but it is of course not truly hidden, as the ix:hidden section in any ESEF report is accessible through various consumption software. Even though it can be accessed, however, there are quite strict limitations on what is allowed within the ix:hidden section.
How does something end up in the ix:hidden section?
Any fact which does not have visual representation in the report will appear in the ix:hidden section. For instance, if the “Name of parent entity” is tagged in your report, but isn’t also specified in the visual layer, it will be placed in the ix:hidden section.
What is allowed in the ix:hidden section?
In July 2021 ESMA updated their reporting manual to specify that the only elements considered not eligible for transformation, are elements for which there are no transformation rule in the latest recommended Transformation Rules Registry, and that the hidden section should not be used as a workaround to tag values containing XHTML markup.
While you can look up facts in the registry individually, it is easier to assume that the hidden section of your report should be empty. Another way to ensure that you don’t have anything illegal in the hidden section, is to upload your finished ESEF file to an ESEF validation tool, such as the ParsePort XBRL Inspector, and see if you have a clean validation. In case of transgression, you will receive this message: Violation: “transformableElementIncludedInHiddenSection”.
Further, it is worth noting, that companies reporting in more than one taxonomy may experience that elements from the secondary taxonomy appear in the ix:hidden section. However, this doesn’t conflict with ESMA’s requirements.
Why are hidden transformable facts an issue?
Some XBRL professionals have voiced their concerns that certain elements may not be eligible for transformation without reducing the quality of the reports, and that the ix:hidden section can be used as a workaround to graphically align these elements.
However, the entire purpose of ESEF is transparency, and whenever information is permitted in the ix:hidden section, it forms a discrepancy between the visual layer and the technical layer of the report in question.
In most cases this discrepancy may be innocent as in the case with a workaround to make sure that certain elements are styled correctly and still mapped, but whether it happens by mistake or malintent, it also gives filers the opportunity report different figures in the visual and technical layer relatively.