Plain language: Provide clear and simple language in instructions, labels, navigational elements, and error messages which require a response to continue, so that all of the following are true.

Simple tense: Use present tense and active voice.
Simple, clear, and common words: Use the most common 1500 words or phrases or, provide words, phrases or abbreviations that are the most-common form to refer to the concept in the identified context.
Double negatives are not used.
Concrete language: Non-literal language is not used, or can be automatically replaced, via an easy-to-set user setting. All meaning must be retained when non-literal text is replaced.
Instructions: Each step in instructions is identified

New exception
If there are no tools available in the language of the content that identify uncommon words, instructions that are longer than 400 words are exempt unless they directly relate to a critical service.

New Glossary item:

identified context: context and a context specific word frequency list (and glossary) have been identified in an accessibility statement or other known technique. A word frequency list has to be generated from at least 1000 sources from the same context or however many pages can reasonably be found.