Suppose an instruction states, “Selected persons should attend,” and a subsequent statement specifies the selection criterion. This illustrates the general idea of bayan al-tafsir: resolving an indeterminate meaning by explanation.
Bayan al-taqrir instead reinforces an existing meaning, while bayan al-taghyir can change the operative scope through an attached condition or exception. Bayan by necessity and bayan by replacement have still other roles. Not every additional sentence is simply “more information.”