each blocks

each <condition> runs its body once for every entity that satisfies a named open condition: a condition whose it is left free, so it describes a set rather than testing one thing. Inside the body, the match is the current entity; it keeps meaning the clause's owner.

define condition frame-seedling: it is a seedling and it is in the cold frame
define condition labeled-pot: it is a pot and it is in the potting shed

  on planting it
    each frame-seedling
      move the match to the Nursery Bed
      phrase planted-out with plant = the match
    end each
    phrase planting-done
  end on

Each matching seedling is moved and announced; then, after the loop, planting-done speaks once. The body is ordinary statements, so move, change, phrase, and the rest all work, and the match is a value you can pass as a parameter (with plant = the match) or use as a move/change target. The iteration order is the order entities were created, and an empty match set simply runs the body zero times.

each blocks nest. The binder the match always refers to the innermost loop:

  on auditing it
    each frame-seedling
      each labeled-pot
        phrase audit-pair with pot = the match
      end each
    end each
  end on

each is legal wherever statements are (on bodies, action bodies, trait clauses, sequence steps) and never at the top level (parse.each-top-level). Its condition must be a declared open condition; a closed condition or a story state is analysis.closed-condition-selection, and the match outside any each body is analysis.match-outside-each. match is a reserved name: you cannot call an entity, alias, trait field, or grammar slot match.