I hear a lot of people, far too commonly auditors, make statements like, "I don't care about creating SEC XBRL financial reports correctly, all I need to do is comply with the EFM rules," Or something to that affect.
Personally, I see things a little differently. For example, if 97.9% of all SEC XBRL financial filings do something one way and only 2.1% take some other approach and that other approach used by that 2.1% is not rational, is illogical, and contradictory; that approach could be difficult to justify.
While it is true that Edgar Filer Manual (EFM) rules are not provided for structuring your financial report representations correctly and while it may be true that the US GAAP Taxonomy Architecture does not do the best job of articulating allowed and disallowed relations; that does not mean that there are not logical and illogical representations of such structures in digital financial reports.
Understanding Model Structure Rules is a document which helps those trying to become XBRL master craftsmen understand the different categories of report elements which many less knowledgeable people incorrectly refer to collectively as "tags". It also helps you understand the sensible, logical, rational relations and avoid contradictions, inconsistencies, and communicating information which simply make no sense at all in your SEC XBRL financial filings.
Here is an example. Consider this screen shot: (see in XBRL viewer here)
If you open the larger image by clicking on the screen shot above you will see that this SEC filer put a [Member] within a set of [Line Items] which makes no sense at all.
The model structure is made up of distinct categories which all the report elements of an SEC XBRL financial filing fit into: Network, Table, Axis, Member, Line Items, Concept, Abstract. There are logical and sensible relations between these different report element categories. Understanding these report element categories and the relations between them will help you realize that the term "tag" does not belong in your vocabulary when it comes to digital financial reporting.
Avoid creating absurd representations of your SEC XBRL financial filings.