feat: documents and session tokens

spec/11-corrections.md

@@ -20,7 +20,7 @@ Each has an `index`, counted from 1 in the order corrections are applied, and th
 | `set` | `target`, `attr`, `value` | Sets one structural attribute: a section's `level`, a table's `columns`, a cell's `column`, `rowspan`, `colspan` or `role`, a row's `header_path`, a list's `ordered`, an item's `marker` or a theorem's `variant`. | Unchanged. |
 
 A leaf's editable strings are the `text` of its `text`, `link`, `cite`, `xref` and `fnmark` runs and the `source` of its `math` runs, each searched on its own; an equation's `source`; a verbatim node's `text`.
-`set` is an addition to the design's eight operations, needed to fix table structure; see [DECISIONS.md](../DECISIONS.md).
+`set` exists because readings drop spans, roles and header paths; see the [rationale](../docs/rationale.md#corrections).
 Runs are made canonical after every operation, and the result MUST satisfy every rule of [3](03-nodes.md).
 
 ## 11.2 Every correction records