Best Practices
Guidelines for creating high-quality iXBRL filings with accurate concept mappings and well-structured extensions.
Concept mapping
Choosing the right taxonomy concept is the most important step in iXBRL tagging. Always search the full taxonomy before considering custom extensions.
- 1.Search the taxonomy thoroughly — check all presentation groups, not just obvious locations.
- 2.Match semantic meaning — don't rely on label similarity alone. Check documentation and relationships.
- 3.Verify period type — balance sheet items are "instant", income statement items are "duration".
- 4.Use extensions as a last resort — excessive extensions reduce comparability and may trigger regulatory scrutiny.
Good practices
- Use specific concepts over generic ones
- Match data types (monetary to monetary)
- Use consistent concepts across periods
- Document why extensions are needed
Common mistakes
- Using "Other" when specific concepts exist
- Same tag for semantically different items
- Creating extensions without searching first
- Anchoring to abstract concepts
Custom extensions
Create custom extensions only when no existing taxonomy concept accurately represents your financial data. This includes unique financial instruments, industry-specific items, or cases where existing concepts are too broad or narrow.
For ESEF filings, extensions in primary financial statements must be anchored to the core taxonomy. See the extension anchoring section.
LC3 naming convention
Extension element names follow the LC3 convention: derived from the standard label, using English CamelCase with no special characters.
Rules
- Start with uppercase, CamelCase format
- Derived from the concept's standard label
- Only ASCII letters and numbers
- Use your company's ticker as prefix (e.g.,
acme:CustomerAcquisitionCosts)
Correct
CustomerAcquisitionCosts
FlightEquipment
Incorrect
customer_acquisition_costs
Other Income
Extension documentation
Every custom extension must include documentation explaining why no existing concept is suitable, the business meaning, and the relationship to existing concepts.
Example
"Represents costs related to acquiring new customers through digital marketing channels. SellingExpense is too broad as it includes all selling activities. Tracked separately for investor reporting."
Duplicate facts
The same fact often appears in multiple places (e.g., Total Assets in both balance sheet and notes). Tag all occurrences, but ensure values are identical.
Consistent duplicates
Same value across all occurrences — acceptable and automatically de-duplicated.
Inconsistent duplicates
Different values for the same concept — causes validation failures, even from minor rounding.
Semantically different items must have different tags, even with similar labels. Use specific concepts or create extensions.