XBRL & ESEF
Extension taxonomy
Also known as: Extension element · Extension concept · Custom concept
A company-specific addition to a base taxonomy, created when an entity reports something no standard concept captures.
What it means
An extension taxonomy is a taxonomy built on top of one or more existing taxonomies (the base taxonomy) as a starting point. An extension element is a company-specific concept created within it when the entity reports a line item whose meaning no base concept captures.
In ESEF, extensions are allowed only where no existing ESEF/IFRS element reflects the intended accounting meaning, and every extension element must be anchored to the closest base element so others can still interpret it.
How it relates to nearby concepts
Extensions sit on top of an XBRL taxonomy and are kept interpretable by anchoring. They are a normal part of tagging a real-world report, where companies rarely fit a standard taxonomy exactly.
Common misunderstandings
- You can create extensions freely: Regulators restrict them to cases where no base concept fits, and they must be anchored to the base taxonomy.
Statera handles extensions and anchoring as part of ESEF preparation. See the framework:
ESEF Digital Filing →Sources
Last reviewed: 19 June 2026
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