Form model

form.json (inside the .dmf) is the canonical form definition. It separates fields (the data model) from layout (how they’re arranged). A minimal renderer only needs fields; a full one walks steps.

Top-level

{
  "id": "contact_form",
  "name": "Contact form",
  "description": "Say hello",
  "schemaVersion": 1,
  "submitPolicy": "Anonymous",
  "fields": [ /* FieldDefinition[] */ ],
  "steps": [ /* Step[] — layout */ ],
  "style": { /* FormStyle */ },
  "cardLayout": { /* optional single-record card view */ },
  "lockedStyleFields": [ /* style paths the author pinned */ ],
  "messages": { "<slotId>": "custom message" }
}

Field	Type	Notes
`id`	string	Stable form id (snake_case).
`name`	string	Display name.
`description`	string?	Optional.
`schemaVersion`	int	Per-form author-managed counter, starts at `1`. Copied into the submission `formVersion`. Not a format version.
`submitPolicy`	string	`"Anonymous"` or `"Authenticated"`.
`fields`	array	The data model — see field kinds.
`steps`	array	Layout tree (below).
`style`	object?	Form-level theme/style (see palette/elementCss in the bundle).
`cardLayout`	object?	Optional layout for the single-record card / page-through view. Renderers that only render the form for submission can ignore it.
`lockedStyleFields`	string[]	Style paths the author explicitly pinned (authoring hint; not needed to render).
`messages`	object?	Form-level message-slot overrides (e.g. a validation banner).

FieldDefinition

Each entry in fields[]:

{
  "id": "f1",
  "name": "email",
  "label": "Email",
  "description": null,
  "placeholder": null,
  "autocomplete": "email",
  "kind": "email",
  "required": true,
  "defaultValue": null,
  "calculatedExpression": null,
  "visibleWhen": null,
  "isPrimaryDisplay": false,
  "indexed": false,
  "validation": [ /* ValidationRule[] */ ],
  "messages": { "<checkId>": "custom error" },
  "style": { /* per-field Style override (optional) */ },
  "labelStyle": { /* per-field label Style override (optional) */ },
  "choice":  { "allowCustom": false, "choices": [ { "value": "a", "label": "A" } ], "display": "Radios", "columns": 2 },
  "number":  { "min": 0, "max": 100, "decimalPlaces": 0, "format": "N0" },
  "money":   { "currency": "EUR", "decimalPlaces": 2 },
  "text":    { "minLength": 0, "maxLength": 200, "pattern": null },
  "scale":   { "min": 1, "max": 5, "minLabel": "Low", "maxLabel": "High", "shape": "Circle" },
  "date":    { "min": "2020-01-01", "max": "2030-12-31" },
  "attachment": { "acceptedExtensions": [".pdf"], "maxSizeBytes": 5000000 },
  "relation": { "targetFormId": "...", "displayFieldId": "...", "multiple": false }
}

name is the storage key used in submission values and expressions.
autocomplete is an optional HTML autocomplete token (e.g. email, name).
kind selects the editor + value shape — see field kinds.
Exactly one kind-specific option block (choice/number/money/scale/…) is populated, matching kind.
calculatedExpression / visibleWhen are DSL strings — see expressions.
isPrimaryDisplay marks the record’s title field; indexed requests a DB index (receiver-side hint).
style / labelStyle are optional per-field design overrides (authoring detail; a structure-only renderer can ignore them).

Layout: steps → sections → rows → columns

Form
└─ steps[]            (one step = one wizard page; render inline if you don't do wizards)
   └─ sections[]
      └─ rows[]        ( columnsPerRow: int = 12 )
         └─ columns[]  ( polymorphic — discriminated by "kind" )

Each Row has columnsPerRow (grid track count, default 12). Each Column carries span (tracks, default 12) and an optional stackBelowPx (stack full-width below that viewport width, default 640). Column kinds (discriminated by kind):

Column kind	Renders
`field`	a field, by `fieldId` → `fields[].id`
`group`	a titled, optionally-collapsible container with nested `rows[]` + its own `visibleWhen`
`richtext`	Markdown block (body in `markdown`)
`image`	a static image (`source`, `altText`, `maxHeight`, `maxWidth`, `align`)
`divider`	an `<hr>` (`thickness`, `color`)
`spacer`	vertical space (`height`)
`heading`	a heading (`text`, `level` 1–4)
`button`	a button — `name` + `label` (required), `action` (`None`/`Submit`/`Save`/`Reset`/`NextStep`/`PrevStep`), `variant`, `iconGlyph`

A field referenced by a field column is rendered where the column sits; fields not placed in any column are typically auto-appended (renderer choice).

Styling

Authoring tools bake resolved styles into the .dmf v3:

elementCss.json — element-key → CSS string (e.g. field/<id>, form/<id>).
palette.css — :root light/dark theme variables.
fonts.css — @font-face for embedded fonts.

A renderer applies these on top of a structural layout layer. Rendering structure-only (ignoring the author’s design) is a valid mode — drop the palette + elementCss and your host’s CSS applies.

See Build your own for a minimal renderer walkthrough.