An archival sheet carrying fields of its own

A records office's reference, the department it came from, the date until which the document must be kept and its classification, in a PDF/A-3 file. No standard knows what a retention date is, so each field arrives with a description of itself — its type, who it is written for, what it means — which is what makes checking software accept information you invented. The page prints the same list, so what a person reads and what a machine reads cannot drift apart.

JSON write_own_schema.json 244 lines

This one is not a program. It is the request the document server is sent: the same page, asked for over the network by an application that writes no PDF code at all.

This request reproduces the page rather than describing it the way the library example does. The library sets the two tables with a tab ruler and a hanging list, which a request cannot ask for: the five names of the second table are placed here one by one, each on the line its description falls on. The page comes out the same to the dot; what is being asked for does not read the same.

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{
  "archive": "pdfa3b",
  "metadata": {
    "title": "Records office cover sheet RO-2026-004318",
    "author": "Olivier Pons",
    "subject": "An archival sheet carrying metadata of its own",
    "producer": "hqf-pdf",
    "created": "2026-07-14T09:30:00+02:00",
    "schemas": [
      {
        "name": "Records Office Schema",
        "namespace": "https://hqf-pdf.example/ns/records/1.0/",
        "prefix": "rec",
        "properties": [
          {
            "name": "Reference",
            "value": "RO-2026-004318",
            "description": "The reference the records office files the dossier under",
            "value_type": "text",
            "category": "external"
          },
          {
            "name": "Department",
            "value": "Planning",
            "description": "The department the dossier came from",
            "value_type": "text",
            "category": "external"
          },
          {
            "name": "RetainUntil",
            "value": "2056-12-31T23:59:59+01:00",
            "description": "The date the dossier may be destroyed, and not before",
            "value_type": "date",
            "category": "internal"
          },
          {
            "name": "Classification",
            "value": "Public",
            "description": "How widely the dossier may be circulated",
            "value_type": "text",
            "category": "external"
          },
          {
            "name": "Sheets",
            "value": "1",
            "description": "How many sheets the dossier holds",
            "value_type": "integer",
            "category": "internal"
          }
        ]
      }
    ]
  },
  "items": [
    {
      "type": "text",
      "rect": {
        "llx": 72.0,
        "lly": 756.0,
        "urx": 523.0,
        "ury": 780.0
      },
      "content": [
        "Records office cover sheet"
      ],
      "font": "DejaVuSans",
      "font_size": 20.0
    },
    {
      "type": "text",
      "rect": {
        "llx": 72.0,
        "lly": 727.0,
        "urx": 523.0,
        "ury": 742.0
      },
      "content": [
        "The fields below are the records office's own. No part of the PDF standard knows what a retention date is, so the file explains itself: each field arrives in the metadata packet with its name, the way it is to be read, who it is written for, and what it means. An archival validator accepts them on that description, and refuses metadata that turns up without one."
      ],
      "font": "DejaVuSans",
      "font_size": 10.5,
      "leading": 15.0,
      "align": "justify"
    },
    {
      "type": "text",
      "rect": {
        "llx": 72.0,
        "lly": 616.6,
        "urx": 523.0,
        "ury": 631.0
      },
      "content": [
        "What the sheet says"
      ],
      "font": "DejaVuSans",
      "font_size": 12.0
    },
    {
      "type": "text",
      "rect": {
        "llx": 72.0,
        "lly": 591.6,
        "urx": 523.0,
        "ury": 608.6
      },
      "content": [
        "Reference\nDepartment\nRetainUntil\nClassification\nSheets"
      ],
      "font": "DejaVuSans",
      "font_size": 11.0,
      "leading": 17.0
    },
    {
      "type": "text",
      "rect": {
        "llx": 222.0,
        "lly": 591.6,
        "urx": 523.0,
        "ury": 608.6
      },
      "content": [
        "RO-2026-004318\nPlanning\n2056-12-31T23:59:59+01:00\nPublic\n1"
      ],
      "font": "DejaVuSans",
      "font_size": 11.0,
      "leading": 17.0
    },
    {
      "type": "text",
      "rect": {
        "llx": 72.0,
        "lly": 489.2,
        "urx": 523.0,
        "ury": 503.6
      },
      "content": [
        "What the packet declares of each of them"
      ],
      "font": "DejaVuSans",
      "font_size": 12.0
    },
    {
      "type": "text",
      "rect": {
        "llx": 222.0,
        "lly": 467.2,
        "urx": 523.0,
        "ury": 481.2
      },
      "content": [
        "Text · external · The reference the records office files the dossier under\nText · external · The department the dossier came from\nDate · internal · The date the dossier may be destroyed, and not before\nText · external · How widely the dossier may be circulated\nInteger · internal · How many sheets the dossier holds"
      ],
      "font": "DejaVuSans",
      "font_size": 9.5,
      "leading": 14.0
    },
    {
      "type": "text",
      "rect": {
        "llx": 72.0,
        "lly": 467.2,
        "urx": 222.0,
        "ury": 478.6
      },
      "content": [
        "rec:Reference"
      ],
      "font": "DejaVuSans",
      "font_size": 9.5
    },
    {
      "type": "text",
      "rect": {
        "llx": 72.0,
        "lly": 439.2,
        "urx": 222.0,
        "ury": 450.6
      },
      "content": [
        "rec:Department"
      ],
      "font": "DejaVuSans",
      "font_size": 9.5
    },
    {
      "type": "text",
      "rect": {
        "llx": 72.0,
        "lly": 425.2,
        "urx": 222.0,
        "ury": 436.6
      },
      "content": [
        "rec:RetainUntil"
      ],
      "font": "DejaVuSans",
      "font_size": 9.5
    },
    {
      "type": "text",
      "rect": {
        "llx": 72.0,
        "lly": 397.2,
        "urx": 222.0,
        "ury": 408.6
      },
      "content": [
        "rec:Classification"
      ],
      "font": "DejaVuSans",
      "font_size": 9.5
    },
    {
      "type": "text",
      "rect": {
        "llx": 72.0,
        "lly": 383.2,
        "urx": 222.0,
        "ury": 394.6
      },
      "content": [
        "rec:Sheets"
      ],
      "font": "DejaVuSans",
      "font_size": 9.5
    },
    {
      "type": "text",
      "rect": {
        "llx": 72.0,
        "lly": 352.2,
        "urx": 523.0,
        "ury": 365.2
      },
      "content": [
        "Every value above is written twice: once on this page, and once in the packet a machine reads, under the prefix the schema names. Reading the file's metadata gives back this table, field for field."
      ],
      "font": "DejaVuSans",
      "font_size": 9.0,
      "leading": 13.0
    }
  ]
}