Diff the Webref CSS data from MDN

This repository serves as a utility to diff the CSS data in w3c/webref from those in mdn/data based on customizable mdn-filters.js, webref-filters.js, and key-coverages.js. It can be used to:

• identify data issues in both sources;
• update the MDN data according to the Webref data.

Using the GitHub Action

A Github Action is provided to generates the diff from @webref/css to mdn-data.

Usage:

1. Navigate to the "Actions" page.
2. Click "diff-data" under "All workflows".
3. In the dropdown menu of the "Run workflow" button, select a branch.
4. Run the action.
5. Download the artifact on the page of this workflow run.

Using the browser console

For more flexibility to customize the data sources, a code snippet is provided below to generate the diff when running in the browser console. The default data sources are the curated branch of w3c/webref and the main branch of mdn/data.

Note: The code snippet requires Firefox ≥ 89, Chrome ≥ 89, or Safari ≥ 15.

Usage:

1. Navigate to the page of any branch of this repository (or any fork of it).

2. Run the following code snippet in the browser console:

   // Uncomment to customize the directories
   // used to fetch MDN and Webref data.
   // self.mdnBase = "https://github.com/mdn/data/raw/main/";
   // self.webrefBase = "https://github.com/w3c/webref/raw/curated/ed/";
   
   (async () => {
     const path = /^((\/[^/]+){2})((\/[^/]+){2})?.*/.exec(location.pathname);
     if (!path) {
       throw new ReferenceError("No base branch found.");
     }
   
     const base = document.createElement("base");
     base.href = `https://github.com${path[1]}/raw${
       path[3] ? path[4] : "/main"
     }/`;
     document.head.prepend(base);
   
     const output = await import("./diff.js");
     for (const key in output) {
       const str = JSON.stringify(output[key], null, 2);
       if (str != "{}") {
         sessionStorage[key] = str;
       }
     }
   
     console.info("Outputs stored in sessionStorage.");
   })();

   Note: The XHR logging can be turned on to monitor the downloading progress.

3. Use console.log() to display the outputs.

Updating mdn/data in coordination

The following procedure can be used to fix or add entries to mdn/data while ensuring consistency with w3c/webref:

1. Make the tentative update in a branch of mdn/data.
2. Use the code snippet in Using the browser console with the value of self.mdnBase changed to the branch that contains the update.
3. Run the code snippet in the browser console.
4. Verify if the updated entries are consistent with w3c/webref.
5. If necessary, modify filters.js and key-coverags.js accordingly, reload the page, and re-run the code snippet for verification.
6. Make a pull request to mdn/data.

Structure of diff.json

diff.json essentially follows the structure of the CSS data in mdn/data.

For any key present in both mdn/data and w3c/webref that differs in the two sources, the key's value is replaced by an object with the mdn and ref keys showing respective values.

Example:

"syntax": {
  "mdn": "[ <integer> && <symbol> ]#",
  "ref": "[ <integer [0,∞]> && <symbol> ]#"
}

If the key is mapped to actual texts by l10n/css.json in mdn/data, the mdn key's value is an object with the key and text keys.

Example:

"computed": {
  "mdn": {
    "key": "asSpecified",
    "text": "as specified"
  },
  "ref": "list, each item a duration"
}

For any key present in mdn/data but absent from w3c/webref, the key's entry is relocated to be under the [[MDN-only]] key on the same level of the original key.

Example:

"order": {
  "mdn": {
    "key": "uniqueOrder",
    "text": "the unique non-ambiguous order defined by the formal grammar"
  },
  "ref": "per grammar"
},
"[[MDN-only]]": {
  "media": "visual"
}

Structure of mdn-filters.js

mdn-filters.js is effectively a JSON file, but wrapped as a module to enable the full syntax of JavaScript, including comments and trailing commas.

Its keys can be any of atrules, functions, properties, selectors, and types, which indicate the types of definitions included in the diff.

Note: Descriptors are not able to be filtered directly since they are not at the top level.

Its values are objects with two optional keys - keys and subkeys, the values of which are arrays.

• The items under keys indicate the definitions included in the diff. If omitted, all definitions are included.
• The items under subkeys indicate the informations under each definitions included in the diff. If omitted, all informations are included.

Example:

"atrules": {
  "keys": [
    "@counter-style",
    "@media"
  ],
  "subkeys": [
    "syntax",
    "descriptors"
  ],
},
"functions": {}

Note: Prefixed definitions will be removed from the diff if not found in w3c/webref. Therefore it is unnecessary to specifically block prefixed definitions.

Structure of webref-filters.js

webref-filters.js is effectively a JSON file, but wrapped as a module to enable the full syntax of JavaScript, including comments and trailing commas.

Its structure is a <filter> as recursively defined below:

<filter> = {
  "[[allow]]"?: [ <key>, …, <key> ],
  "[[block]]"?: [ <key>, …, <key> ],
  <key>*: <filter>
}

where:

• Each <key> representes a string;
• * indicates at least zero occurence of a key;
• ? indicates zero or one occurrence of a key;
• <key>s under allow indicate the keys included at this level, and allow defaults to the array of all keys at this level;
• <key>s under block indicate the keys excluded at this level, and block defaults to the empty array.

Note: If allow and block are both present at the same level, block will be ignored.

The top-level keys are the names of the specification JSONs under ed/css in w3c/webref, which indicate the specifications included for the diff.

Example:

{
  "[[block]]": [
    "css-color-6"
  ],
  "css-fonts": {
    "[[block]]": [
      "types"
    ],
    "atrules": {
      "[[allow]]": [
        "@font-face",
        "@font-palette-values"
      ],
      "@font-face": {
        "descriptors": {
          "[[allow]]": [
            "font-family",
            "src"
          ]
        }
      }
    },
    "properties": {
      "font-weight": {
        "[[block]]": [
          "computed",
          "order"
        ]
      }
    }
  }
}

Structure of key-coverages.js

key-coverages.js is effectively a JSON file, but wrapped as a module to enable the full syntax of JavaScript, including comments and trailing commas.

Its keys are from l10n/css.json in mdn/data, and its values are the text values in w3c/webref that the key should cover.

Example:

"asSpecified": [
  "as specified",
  "specified keyword",
  "specified keyword or a pair of numbers",
  "specified keyword(s)",
  "specified keyword, identifier, and/or integer"
]