The word X in XBRL- stands for ‘extensible’ Business Reporting language. The common question that comes up is, in a reporting language what is extensible?

This short read will give you answers to your questions on what extensible stands for, what should be extended, and when. You may also want to read our previous blog- Essential ESEF iXBRL Tagging Concepts

What is an an Extension?

Issuers are required to follow the ESEF taxonomy for preparing their iXBRL filing that needs to be submitted to the national regulator. In the process of preparing iXBRL documents, issuers are required to map their disclosures in the Primary Financial Statements with an appropriate element in the ESEF taxonomy. There would be some instances where there is no appropriate element available in the ESEF taxonomy since some disclosures are very unique to a company.

In such case what should an issuer do?

Issuers are required to create custom elements (also known as extensions in the world of XBRL) to map such unique disclosures where there is no appropriate element present in the ESEF taxonomy.

Below are some examples to show when an extension is required to be created and when not.

Example 1: Income Statement of ABC Company

Income Statement of ABC Company

Example 2: Income Statement of XYZ Company

Income Statement of XYZ Company

In example 2, there are 2 types of revenue reported- Crude oil and electricity revenue Revenue which is the primary revenue source of the company, and Other Revenue, which is an aggregate of all other ancillary revenue not separately disclosed.

In the ESEF taxonomy, there is a concept named ‘IFRS-full-Revenue’ which is a summation of all revenue, including from primary revenue sources and other revenue sources.

Had the company disclosed only one item under revenue – Crude Oil and Electricity Revenue – the disclosure could have been tagged with the IFRS-full-Revenue tag. However, since there is a residuary revenue disclosed (Other Revenue), tagging Crude Oil and Electricity Revenue to IFRS-full_Revenue is incorrect in this situation.


It is also inappropriate to use the ESEF element ifrs- full_RevenueFromSaleOfCrudeOil since this element does not include revenue from the sale of electricity. Therefore, in such case, there is a need to create an extension element.

An extension element usually has a prefix that is based on the company name, followed by the element name. In this case the extension element ‘xyz_ CrudeOilAndElectricityRevenue’ can be created.

Extension Decision-Making Tree

Extension Decision Making Tree

Extension – Good or Bad?

Well, everything comes with a set of pros and cons, the same is the case with extensions as well.

The good part of extensions is that companies can report the information exactly the way they believe make the most sense for their business. Companies cannot skip reporting information just because the taxonomy does not have such a line item. In other words, extensions allow the company to report all the information in their Primary Financial Statements in digital format, in terms of ESEF iXBRL reporting.

Getting data is better than not having data!

The not-so-good part of extensions is that every company has the flexibility to create and name the extensions the way they want. But screening for regulators becomes tougher as too many extensions get in the way of analysis and bench-marking financial data.

For example, if two companies that seek to extend a disclosure on Mining Revenues could do it completely differently. Company A could report ‘Mining Revenue’ as ‘a_MiningRevenue’, however Company B could report ‘Revenue from mining’ as ‘b_RevenueFromMining’. Though both mean the same thing, the way companies create their extensions could be completely different, and thereby lose the ability to standardize and compare the information. extension

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