Implementing rules are Commission regulations. A regulation is usually composed of a short introductory regulation, colloquially known as ‘cover regulation’, and Annexes thereto, containing the technical requirements for implementation. In the EASA system, these Annexes are usually called Parts (e.g. Part-21 is an annex to Regulation 1702/2003; Part-ORO is an annex to Regulation (EU) No 965/2012).

The ‘cover’ regulation is usually short (a few pages) and it includes:

• The preamble made up of:
  • Citations (the paragraphs introduced by ‘Having regard to…’); and
  • Recitals (clauses introduced by ‘whereas’), explaining the reasons for the contents of the enacting terms (i.e. the articles) of an act, the background principles and considerations that lead the legislator to adopt the regulation;
• The articles of the regulation, which contain:
  • A description of the objective and scope of the regulation;
  • Definitions that are used throughout the regulation and its annexes;
  • The establishment of the applicability of its annex(es);
  • Conversion and transition measures.

Reference: https://www.easa.europa.eu/en/faq/18998