# Registry

The registry holds lists that tools read at run time.
Each list is a data file, so a reader, writer, converter or checker loads it instead of copying it into code, and a team can change a list without changing a program.
This page is for newcomers, implementers who need the exact behavior, and experts who want the status of each format.

| File | Holds |
| --- | --- |
| `formats.json` | Every format: its identifier, media type (null for four formats that have none), schema, status, chapter and a one-line description. |
| `rules.json` | Every validation rule ID, with what it means and the chapter that defines it. |
| `stamps/scienting-stamps-1.json` | The published rules that recognize the download stamps publishers add to PDFs (see Adding stamp rules), so page fingerprints ignore them. |
| `stages/scienting-stages-default.json` | The rights each processing stage needs, as a default a team may replace. |

## Format status

Each entry in `formats.json` has a `status`.
A `candidate` format is complete, with vectors and fixtures, and ready to implement.
It changes only with a recorded reason and a new or changed vector.
A `provisional` format is complete and expected to change as implementations gain experience, so it may change more freely.
At version 0.1.0, 20 of the 27 formats are `candidate` and seven are `provisional`.
The third defined value, `reserved`, is unused.
The values are defined in [Chapter 0, section 0.4](../spec/00-introduction.md#04-status), and the stability rules in [Chapter 22, section 22.5](../spec/22-conformance.md#225-stability).

## Rule IDs

A validator checks a package and reports each failure as `path:line: rule: message`, for example:

```text
nodes.jsonl:6: doc.hash.node-hash: node_hash does not recompute
```

A `node_hash` is a hash (a fixed-length value computed from content, so any change to the content changes it) stored with each node of a document.
The line above is the failure that `fixtures/invalid/hash-mismatch/` is built to cause: its sixth node record carries a `node_hash` of all zeros.

A rule's meaning never changes, and a retired rule's ID is never reused, so tools and people can rely on the IDs.
A tool can match on the `rule` field, whose meaning is looked up in `rules.json`, and treat the message as text for people.
[Chapter 22, section 22.4](../spec/22-conformance.md#224-rules) lists the ID prefixes.
Each directory in `fixtures/invalid/` has an `expect.json` that names the rule it breaks.
The reference checker (`tools/check.py`) fails if that rule is not in `rules.json`.

## Adding stamp rules

Many publishers add a line to each PDF they serve, naming the institution and the time of download.
This page calls that line a stamp.
Two downloads of one paper then differ, so a hash of the file cannot match them.
A page fingerprint is a hash of a page's size, its text and its images.
It is computed after removing every line that a stamp rule matches ([Chapter 7, section 7.1](../spec/07-geometry.md#71-page-fingerprints)).
The vectors in `vectors/fingerprints.jsonl` show this: `acs-download-1` and `acs-download-2` differ in the institution and the time on their stamp lines and have the same fingerprint.

Suppose two downloads of one paper differ only in a stamp line that no published rule recognizes.
Record a rule in a file of your own, marked as learned:

```json
{"format": "scienting-stamps/1", "id": "smithlab-learned", "learned": true,
 "rules": [{"id": "licensed-to", "pattern": "^This copy is licensed to .+", "where": "margin", "margin": 36}]}
```

Normalized text is the line after Unicode Normalization Form C, with each run of whitespace replaced by one space and the ends trimmed ([Chapter 1, section 1.4](../spec/01-conventions.md#14-text-normalization-for-hashing)).

A rule has an `id`, a `pattern`, and a `where` that is `any` or `margin`.
A `margin` rule matches only lines whose box lies wholly within `margin` points of one page edge (36 when the rule gives none).
Patterns use only syntax that ECMAScript and Python read alike, and match a line's normalized text, with the ASCII letters A to Z compared without case.
The allowed syntax is literals, `.`, `*`, `+`, `?`, `^`, `$`, classes and escaped punctuation.

A page record in `pages.jsonl` lists, in `stamps_removed`, the IDs of the rules that removed lines.
A rule that is too broad hides a real difference between two pages.
A stamp that no rule recognizes splits one edition into two ([Chapter 7, section 7.2](../spec/07-geometry.md#72-stamp-rules)).

## Replacing the stage defaults

A stage is one step of processing, such as conversion or indexing.
Each stage needs certain rights, such as the right to mine text, and a stage runs only when the rights record of the paper allows them.
The stage requirements are configuration, not code, because what a team may do depends on how it holds each paper.

A team copies `scienting-stages-default.json`, adjusts it with its counsel and points its project's settings at the copy.
The file itself calls its contents "proposed defaults from the design, for counsel to set".
In a project, the `settings.stages` field holds the `id` of the stage file in use ([Chapter 20](../spec/20-projects.md)), so a team's copy needs an `id` of its own.
The project format is `provisional`.
[Chapter 14](../spec/14-rights.md) explains how stages are checked.