This document is a review draft. Readers are invited to submit comments to the Implementation Guidance Task Force.
Table of Contents
- 1 Introduction
- 2 Scope
- 3 Filing Rules
- 3.1 Naming of taxonomy components
- 3.2 Types of elements to be extended
- 3.3 Custom Taxonomy components
- 3.4 Taxonomy Labels and References
- 3.5 Extension taxonomy relationships
- 3.6 Construction of an extension taxonomy
- 4 Guidance for Taxonomy Extension
- 5 Summary
Whilst some filing rules are necessary in order to ensure correct and reliable operation of the filing system, XBRL best practice recommends minimising their use as they create a burden for software developers and preparers, and can create interoperability issues.
This guidance provides a checklist which may be used to define filing rules for taxonomy extension by preparers. The rules in the checklist generally focus on syntactical and technical aspects of extension taxonomy. This guidance is targeted towards XBRL and iXBRL report collectors who allow preparers to extend their base taxonomy.
Filing rules to constrain taxonomy extension are required to ensure:
- unsupported technical features are not used;
- preparers do not make inappropriate modifications to base taxonomy components;
- data quality errors are reduced; and
- taxonomy extensions are created consistently across filers.
This checklist is intended to be used as a reference when defining filing rules for an XBRL reporting programme. The filing rules discussed in this document are provided as guidance only; data collectors should consider whether each rule is necessary and applicable to their reporting system.
A separate piece of guidance discusses the broad principles for creation and publication of filing rules and there is also a checklist for XBRL report filing rules.
This guidance assumes that the data collector has made the decision to allow extension taxonomies. The task force studied the EDGAR Filer Manual (US SEC) and the draft European Single Electronic Format (ESEF) Reporting Manual. The task force seeks comments on other filing manuals for taxonomy extension, which can be analysed to improve this guidance.
3 Filing Rules
This section describes filing rules for different categories, such as those related to naming taxonomy components, constraints on extended elements, relationships in the extension taxonomy and construction of the extension taxonomy.
3.1 Naming of taxonomy components
Filing rules may specify formats to be applied when naming extension taxonomy components to ensure consistency across preparers. Such naming conventions need to satisfy constraints imposed by the specification.
3.1.1 Namespaces, arcroles and roles
The namespaces for an extension taxonomy schema usually follow a pattern that identifies the entity and version or reporting period. Extended arcroles and link roles typically adopt a similar pattern to the namespace, suffixed with an identifier for the arcrole or link role.
Filing rules may specify naming conventions for these components which typically require the inclusion of a version date or number, and a unique identifier for the preparer such as a domain name or stock exchange symbol.
The following is an example of a namespace and link role in an extension taxonomy prepared by 'Nokia Corp' for its 'Annual and transition report' submission to the US-SEC.
- Namespace - http://www.nokia.com/20181231
- Role - http://www.nokia.com/role/StatementConsolidatedIncomeStatement
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