ESEF Digital Tagging

The European Single Electronic Format (ESEF) is the EU-mandated single electronic reporting format for the annual financial reports of companies whose securities are traded on a regulated market. It is based on Article 4(7) of the Transparency Directive 2004/109/EC and specified in detail by Delegated Regulation (EU) 2019/815 (the ESEF RTS). Reports must be prepared as XHTML documents; the consolidated financial statements are tagged using Inline XBRL (iXBRL) so that they are both human-readable and machine-readable. Tagging follows a defined taxonomy that uniquely identifies each reported item.

The Corporate Sustainability Reporting Directive (CSRD) extends the digital tagging obligation to sustainability reporting. Companies will also have to tag, in machine-readable form, the sustainability information prepared under the ESRS and presented in the management report. To enable this, EFRAG is developing a digital ESRS taxonomy in cooperation with ESMA, linking every quantitative and qualitative ESRS data point to a unique XBRL element. The ESEF RTS is being amended accordingly so that financial and sustainability information can be combined in a single iXBRL document.

In practice, the tagging obligation means that sustainability data points must not only exist in substance but also be stored in a structured, taxonomy-compliant way. Block tagging captures coherent passages of text, while detail tagging covers individual numeric and categorical values. Supervisors, investors and data providers can then read, compare and check the disclosures automatically. Implementation requires clean data management, a consistent mapping to the ESRS data points and validation steps before submission; tagging errors can undermine assurance and acceptance by the competent authority.