Anchoring is one of the most critical and commonly misunderstood aspects of ESEF compliance. This guide explains what anchoring is, why it matters, and how to do it correctly to avoid validation failures.
Key Takeaways
- All extension elements must be anchored
- Use the wider-narrower arc role
- Select semantically closest base elements
- Multiple anchors are allowed
- Anchoring enables cross-company comparability
What is Anchoring?
Anchoring creates a semantic link between your extension concepts and the base ESEF taxonomy. It tells users: 'my custom element is a more specific version of this standard concept.'
This enables:
• Automated comparability analysis
• Understanding of custom elements
• Data aggregation across companies
Anchoring Requirements
ESMA requires:
• Every extension element must have at least one anchor
• Use the 'wider-narrower' arc role
• Anchor to non-deprecated base elements
• The relationship should be semantically valid
Missing or invalid anchors cause ESEF validation error 2.5.1.
Selecting Anchor Targets
To select the right anchor:
1. Understand your extension's meaning
2. Search base taxonomy for related concepts
3. Choose the closest semantic match
4. Verify the element is not deprecated
5. Consider multiple anchors if applicable
The anchor should represent what your element would be classified as in standard reporting.
Implementation
Anchoring is implemented in the definition linkbase:
<definitionArc
xlink:from="loc_base_element"
xlink:to="loc_extension_element"
xlink:arcrole="http://www.esma.europa.eu/xbrl/esef/arcrole/wider-narrower"
/>
The base element is 'from' (wider), extension is 'to' (narrower).
Common Errors
Avoid these anchoring mistakes: Anchoring to deprecated elements, reversing the wider-narrower direction, anchoring to elements of different types (e.g., monetary to text), creating circular anchor chains, and forgetting to anchor abstract elements.