Here is the EU law that mandates the European Single Electronic Format (ESEF) and mandates that the financial statements be submitted to the European Securities and Markets Authority (ESMA) using Inline XBRL.
Fortunately, the ESMA will be using an approach that is very similar to the U.S. SEC's approach to XBRL-based financial reports with a couple of incremental improvements. The ESEF introduces the notion of "anchoring" and "wider-narrower" concepts. So, that is good.
However, other information is still not represented that is necessary (see the ontology spectrum) to help assure quality XBRL-based financial reports. As such, you can expect quality issues simiar to the quality issues being experienced by the U.S. SEC XBRL-based financial reports. The ESMA field test already shows quality issues when the 23 reports are run through a good validator.
This is kind of disappointing but not really unexpected. When people keep seeing the same issues appear over, and over, and over; perhaps these regulators will figure out that they need to modify their approach. Some times people need to learn by making their own mistakes. But I really don't see why the ESMA did not learn from the SEC's mistakes.
Also, today each different regulator creates their own approach to XBRL-based digital financial reporting. Why is that necessary? If you look at the high-level financial accounting concepts of different reporting schemes, they are essentially very similar or even identical.
Why the inconsistencies between different regulators? These inconsistencies are unjustifiable. What if someone created a standard approach to business and financial reporting? Well, the Object Management Group (OMG) is creating such a standard. You can find information about that proposed OMG standard, Standard Business Report Model (SBRM) here.
Why are the ESMA and SEC both making these mistakes? I suspect that it has to do with the four misconceptions most people have about XBRL-based reports in general.