The European Commission’s readability guideline
This is the core text for anybody drafting leaflets or needing to run usability testing in Europe. It is often known simply as the European guideline. Legally, it is more significant than any of the individual regulators’ guidelines (eg ANSM, BfArM, EMA or MHRA), and it’s relatively concise at 27 pages. It sets out legal obligations, some practical guidance on leaflets, and a suggested test method. Free PDF download.