# 18. Layers and annotations

Everything people and models add to a document is an annotation, and annotations are grouped in layers.
`scienting-layer/1` is the W3C Web Annotation Data Model with the anchor as a selector, so any Web Annotation tool can read it.
The JSON-LD context is [context/scienting-1.jsonld](../context/scienting-1.jsonld), published at `https://paperspec.scient.ing/context/scienting-1.jsonld`.

## 18.1 One rule decides what is a claim and what is a layer

If a statement is true independently of this paper, it belongs in a claim store as a claim, where it is checked and leveled.
If it is about reading this paper, it belongs in a layer, where it is attributed and signed but not checked.

## 18.2 The layer

A layer is a folder with `layer.json` and `annotations.jsonl`.
`layer.json` is an `AnnotationCollection` with the two contexts, `format`, an `id` of the form `tag:scient.ing,2026:layer:<store>/<record id>`, a `label`, a `purpose`, an `audience` (`novice`, `student`, `expert` or `mixed`), a `visibility` (`private`, `team` or `public`), a `license` (CC BY 4.0 by default when public), its `creator`, `created`, its `project`, the `docs` it annotates and its `total`.
A reader turns layers on and off, and the audience dial picks the level of glosses.

## 18.3 The annotation

Each line of `annotations.jsonl` is a W3C `Annotation`:

| Property | Holds |
| --- | --- |
| `@context` | `["http://www.w3.org/ns/anno.jsonld", "https://paperspec.scient.ing/context/scienting-1.jsonld"]`. |
| `id` | `tag:scient.ing,2026:annotation:<store>/<record id>` ([4.6](04-identity.md#46-record-ids)). |
| `type`, `layer` | `Annotation`, and the layer's ID. |
| `motivation` | A W3C motivation: `commenting`, `describing`, `linking`, `questioning`, `assessing`, `replying` and the others. |
| `creator`, `created`, `modified` | An agent `{id, type, name}`, with `type` `Person` or `Software`, and times. |
| `body` | One body ([18.4](#184-bodies)). |
| `target` | A `SpecificResource` whose `source` is `tag:scient.ing,2026:doc:<store>/<key>` and whose `selector` lists an `AnchorSelector` holding a `scienting-anchor/1`, optionally followed by a W3C `TextQuoteSelector` for tools that do not know ours; or, for a reply, a `SpecificResource` whose source is another annotation. |
| `status` | `proposed`, `confirmed`, `rejected` or `withdrawn`. A model's annotation is `proposed` until a person confirms it. |
| `receipt` | For a confirmed annotation, the receipt that covers it. |

The `TextQuoteSelector`, when present, repeats the anchor quote's `exact`, `prefix` and `suffix`, with an empty string for a `prefix` or `suffix` the quote lacks.
It is present only when the anchor's quote is plain text; an anchor whose quote is hashed or keyed ([6.3](06-anchors.md#63-keyed-anchors)) has none, so the fallback never shows text the anchor withholds.

An annotation's content hash is SHA-256 of the canonical JSON of the annotation without `status`, `receipt` and `modified`.
A confirmed annotation is covered by its confirmer's receipt, which lists `["annotation", <record id>, <content hash>]`.
Replies are annotations that target annotations, so discussions are threads anchored to sentences.

## 18.4 Bodies

| `kind` | W3C type | Adds | Says |
| --- | --- | --- | --- |
| `gloss` | `TextualBody` | `audience` | An explanation at `novice`, `student` or `expert` level. |
| `claim-link` | `SpecificResource` | `source`, `pin`, `role` | That the span `states`, `uses` or `disputes` a claim. |
| `symbol` | `SpecificResource` | `source`, `pin`, `key`, `symbol` | That this occurrence of a symbol, the one whose key is `key`, is the symbol a symbol claim defines. |
| `comment` | `TextualBody` | `category` | A remark, opinion or interpretation. |
| `caveat` | `TextualBody` | `category` | A warning a reader should see. |
| `question` | `TextualBody` | `for`, `category` | A question for a `reader`, a `group` or the `authors`. |
| `exercise` | `TextualBody` | `exercise` | A task with a key and a rule ([19](19-exercises.md)). |
| `citation-context` | `TextualBody` | `reference`, `verdict`, `reason` | Why a sentence cites a reference, and whether it supports it. |
| `prerequisite` | `SpecificResource` | `source` | What to read or know first. |
| `crosslink` | `SpecificResource` | `source`, `selector` | That the span corresponds to a span in another document. |
| `translation` | `TextualBody` | `language` | The span in another language. |
| `description` | `TextualBody` | `role` | A description of a figure, panel or table for readers who cannot see it: `alt`, a short text equivalent, or `long`, a full description. |
| `generated` | `TextualBody` | `generator` | Text a model wrote about the span; never mistaken for source. `generator` is `{model, run}` as a correction's model author is ([11.2](11-corrections.md#112-every-correction-records)). |

A textual body has a `value`, and optionally a `format` (`text/plain` or `text/markdown`) and a `language`.

The `source` of a `claim-link` or `symbol` body is a claim in a lode claim store, written as lode writes a reference: `lode:` and the claim's tag, eight Crockford base32 capitals (the digits and the letters without I, L, O and U), as in `lode:272XTX7C`, or `lode:<host>/<tag>` for a claim in another store, `<host>` being a domain name.
A tag never changes, while a claim's slug, such as `amber/k-bond`, may be renamed, so a slug is never a reference.
The optional `pin` fixes the claim as the annotator read it: the same reference, `@`, and the first six lowercase hex digits of the claim's statement hash, as in `lode:272XTX7C@02f47b`.
`common.schema.json` defines both, as `claimRef` and `claimPin`.

A `symbol` body names its symbol twice, as the target's span and by `key`, the symbol's key in the math form `scienting-math/1` ([9.4](09-figures-tables-equations.md#94-the-math-form)), which a claim store gives the symbol a symbol claim defines: `K_{r}` for a span `$K_r$`.
So a reader finds every occurrence of a symbol across a library by its key, however its source spaced or braced it, and a claim store matches the annotation to its claim without parsing the span.
The span is still required, since the key says which symbol and the span says where; `symbol`, optional, is the symbol as the span writes it.

A `comment`, `caveat` or `question` body MAY carry a `category`, which says what it is about, from a fixed list:

| `category` | Says |
| --- | --- |
| `comment` | A general remark. |
| `context` | Background, related work, or what a reader should know to follow the span. |
| `critique` | A flaw in the method, the analysis or the argument. |
| `question` | A question. |
| `correction` | An error of fact, number, citation or reference in the paper. |
| `feedback` | A suggestion addressed to the authors. |
| `resource` | Data, code or a related paper. |

A producer that supports categories SHOULD set one on every comment, caveat and question; the property is optional only so that layers written before it stay valid.
The category is independent of the kind, so a caveat may be a `correction` and a question a `critique`.
A `correction` category says that a reader found an error in the paper; correcting the document's reading of it is a correction of [11](11-corrections.md).
The store's `annotations` table keeps the category beside the body's kind ([13.4](13-database.md#134-the-store-tables)).
Nothing a model writes is ever stored as source text.
A model may propose a `description`, and like any annotation it stays `proposed` until a person confirms it; an accessible export uses confirmed descriptions only, and a figure with none has no description.
Other text a model writes about a span, such as a summary, is a `generated` annotation, which names its `generator`.
`fixtures/records/layer/` holds a layer with one annotation of each common kind, each comment, caveat and question with its category, a claim link and a symbol that reference a lode claim and pin it, and the receipt that confirms some of them.