Don't get me wrong, it's great that @calixteman wanted to implement that — JS should definitely be supported! I don't want to come off as rude or attacking.

For starters, JS reference specified in the [commit comment](https://github.com/mozilla/pdf.js/commit/8de98079ca05f8f7001ee077771055a57dc0e948) is outdated. It's version 8.1 from 2007… We're more than decade past that now. We should be implementing [Acrobat DC SDK](https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/AcrobatDC_js_api_reference.pdf) ([here](https://help.adobe.com/en_US/acrobat/acrobat_dc_sdk/2015/HTMLHelp/#t=Acro12_MasterBook%2FJS_API_AcroJS%2FJavaScript_API.htm) in a nice HTML version).

Other than that, the Doc object now is only implemented with `info` property with standard fields (`Title`, `Author`, `Subject`, `Keywords`, `Creator`, `Producer`, `CreationDate`, `ModDate` and `Trapped`, case insensitive). But [according to the spec](https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/AcrobatDC_js_api_reference.pdf#page=243) (even [in that old version](https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/js_api_reference.pdf#page=243)), this object can contain other, non-standard properties, that can be set both in Acrobat interface and in JS (which are case-sensitive then).

Acrobat 9.0 introduced another field to that property, `Authors`, containing semicolon-delimited list of authors.

There are probably other problems with that code due to the outdated spec @calixteman was apparently working on.
expect(metadata.has("dc:title")).toBeTruthy();
    expect(metadata.has("dc:qux")).toBeFalsy();
    expect(metadata.get("dc:title")).toEqual("'Foo bar baz'");
    expect(metadata.get("dc:qux")).toEqual(null);
    expect(metadata.getAll()).toEqual({ "dc:title": "'Foo bar baz'" });
  });
  it("should gracefully handle unbalanced end tags (issue 10410)", function () {
    const data =
      '<?xpacket begin="Ã¯Â»Â¿" id="W5M0MpCehiHzreSzNTczkc9d"?>' +
      '<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">' +
      '<rdf:Description rdf:about="" ' +
      'xmlns:pdf="http://ns.adobe.com/pdf/1.3/">' +
      "<pdf:Producer>Soda PDF 5</pdf:Producer></rdf:Description>" +
      '<rdf:Description rdf:about="" ' +
      'xmlns:xap="http://ns.adobe.com/xap/1.0/">' +
      "<xap:CreateDate>2018-10-02T08:14:49-05:00</xap:CreateDate>" +
      "<xap:CreatorTool>Soda PDF 5</xap:CreatorTool>" +
      "<xap:MetadataDate>2018-10-02T08:14:49-05:00</xap:MetadataDate> " +
      "<xap:ModifyDate>2018-10-02T08:14:49-05:00</xap:ModifyDate>" +
      '</rdf:Description><rdf:Description rdf:about="" ' +
      'xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/">' +
      "<xmpMM:DocumentID>uuid:00000000-1c84-3cf9-89ba-bef0e729c831" +
      "</xmpMM:DocumentID></rdf:Description>" +
      '</rdf:RDF></x:xmpmeta><?xpacket end="w"?>';
    const metadata = new Metadata(data);
    expect(isEmptyObj(metadata.getAll())).toEqual(true);
  });
  it("should not be vulnerable to the billion laughs attack", function () {
    const data =
      '<?xml version="1.0"?>' +