Data binding & formatting

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Templates bind runtime data (params.json/params.yml) into items three ways, and format values for display via the locale pack.

The three binding forms

data: binding — a single bound value on text, qr_code, image, and (as the array source) table / repeat / repeat_flow / list:

yaml

data: { key: order.code }              # params key, dot-separated
data: { key: amount.total, format: currency }

Interpolation — inside a static text: string on text and qr_code items:

yaml

text: "合計 {amount.total_in_tax:currency} です"

{key} inserts the value; {key:format} applies a format; {{ escapes a literal {. Keys are [A-Za-z0-9_.], format names [A-Za-z0-9_-]. Malformed expressions (unclosed braces, invalid characters, empty key) stay as literal text — templates degrade visibly, never fail. ({{key}} in this documentation names the general interpolation mechanism.)

Named binding declarations — an item-local bindings: map giving one {name} the full data: option set (another key, a scope, a placeholder, a format):

yaml

- type: text
  text: "コード: {code} / 合計 {total}"
  bindings:
    code:  { key: order.code, scope: document }
    total: { key: amount.total, format: currency, placeholder: "—" }

See Named binding declarations below.

Blank-form placeholder

A binding draws a placeholder when its value is absent, null, or "", instead of leaving the field empty and emitting missing_data / format_error. This is the "this field is intentionally blank" signal a fillable form needs — one template renders both a blank form and a filled one from two params files.

yaml

# on the placement (templates.yml):
data: { key: birth_date, format: wareki, placeholder: "　年　月　日" }

yaml

# on the field (definitions.yml) — also covers {key} interpolation:
- key: birth_date
  type: date
  placeholder: "　年　月　日"

Effective placeholder: the placement's data.placeholder wins; otherwise the field's placeholder from definitions. An inline {key} / {key:format} interpolation segment carries no placeholder of its own, so only the field-level one reaches it.
Drawn verbatim: the placeholder text is never interpolated and never formatted — a {…} inside it stays literal, and it bypasses the type formatter entirely. placeholder: "" suppresses the diagnostic and draws nothing (a clean blank).
Blank ≠ invalid: only an absent/null/"" value triggers the placeholder. A value that is PRESENT but unusable (a "abc" date) still reports format_error — a data bug must not hide behind a blank-form placeholder. Whitespace (" "), 0, and false are real values, not blanks.
Applies wherever a binding resolves: text data:, spans, qr_code, char_grid, table columns (per row), and list entry templates (a blank entry field draws its field-level placeholder). Images have no text placeholder — an absent image key stays missing_data.

Capability key: binding.placeholder.

Where `{…}` resolves — not always params

Several other keys reuse the {…} spelling with a different scope:

Where	`{…}` resolves against
`text:` on `text` / `qr_code`	params (or the bound element inside a repeat cell/card)
`list.text`	the array entry object (`{name}` = entry field)
`list.overflowText`	the engine token `{count}` only
`page_number.format`	the engine tokens `{page}` / `{pages}` only

Each surface knows only its own scope: a params key in page_number.format (or {page} in a text:) is not resolved there.

Scopes

Bindings resolve against top-level params by default. Three constructs re-scope them to an array element:

a table column's data.key is relative to the row object;
a repeat cell's bindings resolve against the bound element;
a repeat_flow card's bindings likewise.

validate checks scoped bindings against the array group in definitions.

`scope:` — the escape back to the document

A value that belongs to the whole document rather than the element (a store name on every ticket, one pickup date across a card list) takes the explicit escape:

yaml

- type: text
  data: { key: store_name, scope: document }   # element (default) | document

element (the default, and what every template authored before the key existed means) reads the ambient scope: the bound element inside one of the three constructs, top-level params everywhere else.
document reads top-level params even inside a construct. Outside one the two are identical, and document is deliberately inert there — a sub-template must compose the same way in and out of a repeat.

The key rides every binding carrier: text / spans / qr_code / char_grid / image / a list's array key / a table column's data:, and a form mark's presence binding (ellipse / checkbox data:). validate follows it — a document-scoped key is checked against the top-level scalars (declared field, format variant, params presence) instead of the array group, so the escape never opens an unchecked path.

A bare {key} carries no scope. The {key:format} grammar stays two-part by design, so an UNDECLARED name inside a cell always reads the ambient scope. To mix scopes on one line, declare the name — that is what bindings: is for:

yaml

- type: text
  text: "{shop} / {code}"
  bindings:
    shop: { key: store_name, scope: document }   # the document's value
  # `code` is undeclared, so it stays the element's own field

(spans with a data: per fragment also works and predates declarations, but spans exists for per-fragment styling; reach for it when the fragments differ in appearance, not merely in scope.)

Capability key: binding.scope (older engines parse-reject it).

Named binding declarations

bindings: is an item-local map of interpolation name → the same options a data: binding carries. A declared {name} resolves through its declaration; an undeclared name keeps its original meaning — the name is the key, read at the ambient scope — so every template written before this key existed is unaffected.

yaml

- type: text
  text: "品名: {hinmei} / 合計 {total}"
  bindings:
    hinmei: { key: 品名 }                              # a key the {…} charset cannot spell
    total:  { key: amount.total, format: currency }

It solves two things a bare {key} cannot express:

Keys outside [A-Za-z0-9_.]. {品名} is not a valid expression, so it prints its own braces on the page — silently, until the interpolation_key_charset warning. A declaration gives the key an ASCII name to be referenced by.
Options on an interpolated value: scope: (the escape out of a cell), placeholder:, format:.

Rules:

Which items carry it: text (its spans included), qr_code, char_grid, list (its per-entry text), and image (its link.url only). A span has no map of its own — it resolves through the map of the item that owns it. The map also covers each item's link.url.
A declared name and data.key are separate namespaces. A data: binding already carries every option and never consults the map.
An inline :format wins over the declaration's format (most-specific, like the style cascade). Everything else — the key, the scope, the placeholder — comes from the declaration.
A list's declarations resolve per ENTRY like the entry template itself, unless one authors scope: document.
Bounded by 256 declarations per item (too_many_bindings, advisory — every declaration keeps working).

Diagnostics: unused_binding (declared, referenced by nothing), binding_shadows_key (the name already resolved and the declaration redirects it — attaching options to the same key is silent), invalid_binding_name (a name outside the reference charset, so nothing could ever reference it). A declaration whose key: does not exist rides the usual unknown_data_key, reported at the declaration.

Capability key: binding.declarations (older engines parse-reject it).

Params

Runtime data owned by the calling application, close to ISO-normalized values: ISO/RFC 3339 datetimes, yyyy-mm-dd dates, plain numbers — display formatting is the engine's job. Params never supply geometry: all x/y/w/h are template-owned.

Formats

The format variant (or {key:format}) selects how a value renders:

A field type name overrides the type entirely: string, number, currency, datetime, date, quantity, percentage. Type names are reserved — a formats: registry entry cannot use one.
A named variant: a template formats: registry name, a lang-pack pattern name (ja, long, wareki), or a currency variant (default / symbol / name). Lookup order: registry → pack. An unknown variant renders the default form and warns (unknown_format_variant).
symbol/name on a plain number promote the value to the currency type with that variant (the code rides the defaults.currency chain), so a money display needs no definitions type — the picks work on an untyped params number. This coercion wins over a registry entry that happens to be named symbol/name (registry patterns are date patterns and never applied to numbers). Capability key: format.currency.coerce; older engines warn unknown_format_variant and render the bare number.
value on a field with enum display labels renders the machine value instead of the declared label (definitions.md § Enum display labels). The label is the default the moment the field declares one — on every carrier, a QR code's encoded content included (a QR has always encoded the FORMATTED value). On a field with no labels a format pick stays inert, as it always has (plain text has no variants of its own); on a labeled field an unknown pick warns unknown_format_variant and renders the label.

Precedence (the effective format)

Low → high; the highest layer that picks wins:

the locale pack's default pattern,
the template's defaults.formats.<type> (defaults.md),
the field's displayFormat: in definitions (per-field default),
the placement's format: / {key:format}.

Patterns themselves may be authored ONLY in the central places — the template's defaults/formats: registry and locale packs; placements and definitions always reference by name (the guard against per-item format sprawl).

Per type (locale data = the builtin pack for the locale, with an optional packs/locale/<id>.yml per-key overlay — see fonts.md):

Type	Rendering
`string`	as-is; a declared enum label replaces the value it labels (`format: value` escapes back)
`number`	grouped digits (locale separators); no explicit precision trims trailing zeros (max 2 decimals). A `symbol`/`name` pick promotes the value to `currency` with that variant
`currency`	three named variants: `default` = the bare grouped amount (composes with literals), `symbol` = `¥9,000`, `name` = `9,000円`. Precision: the field's `precision:` → the pack's per-code override → the CLDR fractions table (an unlisted code keeps its digits). Code chain: the field's `currency:` → the template `defaults.currency` → pack `currencyDefault`
`datetime`	CLDR-subset pattern tokens (below); default `yyyy-MM-dd HH:mm`
`date`	same tokens; default `yyyy-MM-dd`
`quantity`	number + the unit word for the field's semantic `unit:` key (`item` when unset), plural-aware via the pack (`1 item` / `3 items`); layout from the pack's `unitFormat`. Unknown keys render verbatim + `unknown_unit`
`percentage`	value × 100 through the locale separators + the pack's `percentFormat` layout

There are no business-document formats beyond these — e.g. no dedicated Japanese qualified-invoice helpers such as per-tax-rate subtotal rows or registration-number fields. Compose them from the primitives (a table + currency/percentage fields, plain text for the registration number); business/region-specific formatters are future plugins/ territory, never engine features (agents/plugins.md).

A fixed summary block (the subtotal/tax/total rows every invoice needs) is NOT a table: table.data binds an array property, while totals are scalar object fields — and the engine does no arithmetic, so the computed values arrive pre-summed in params. The idiom is a container of interpolated text lines (the amounts pick a currency variant in-place):

yaml

- type: container
  box: { w: 240, h: 60 }              # or a right-aligned flow child
  items:
    - type: text
      box: { x: 0, y: 0, w: "100%", h: 14 }
      text: "小計 {totals.subtotal:symbol}"
      style: { textAlign: right }
    - type: text
      box: { x: 0, y: 15, w: "100%", h: 14 }
      text: "消費税(10%) {totals.tax:symbol}"
      style: { textAlign: right }
    - type: text
      box: { x: 0, y: 32, w: "100%", h: 18 }
      text: "合計(税込) {totals.total:symbol}"
      style: { textAlign: right, fontWeight: bold, fontSize: 13 }

(Label + value as separate columns instead: make each line a direction: row child with justifyContent: space_between — flex.md.)

Pattern tokens (append-only inventory)

yyyy y MMMM MMM MM M dd d EEEE E HH H hh h mm ss a GG G — a CLDR subset. MMM/MMMM = month names, EEEE = full weekday, h/hh + a = the 12-hour clock with the pack's dayPeriods, G/GG/y = the era set (below). Text between ' quotes is literal ('at'), '' is a literal apostrophe; unquoted non-token characters pass through, so Japanese pattern text needs no quoting. The inventory is append-only: existing tokens never change meaning, new ones only extend it.

Era formatting (wareki)

G renders the era name, GG its abbreviation (令和 → R, falling back to the name), and y the era year, from the locale's eras table (builtin ja-JP: Meiji through Reiwa). The builtin ja-JP pack ships wareki variants (令和7年4月1日) and a wareki-compact variant (R7.4.1). Year 1 renders as the pack's eraYearOne (ja: 元 → 令和元年); a date before every era falls back — G/GG to empty, y to the Gregorian year. yyyy stays the Gregorian year in any pattern.

Without definitions, the type is inferred from the JSON value (RFC 3339 strings become datetimes, yyyy-mm-dd strings dates, numbers numbers).

Definitions (`definitions.yml`)

The data dictionary for the Designer/AI/validation — not required at render time. An OpenAPI-style schema isomorphic to the params JSON (see definitions.md): nested properties with JSON-Schema types, format as the data-semantic hint, title, example, displayFormat (the field's default variant), displayFormats (declared variants for the GUI picker), currency, precision, unit (a semantic key like item — display words live in the locale pack, so adding a locale never edits definitions), labeled enum members ({ value, label } — the CALLER's display words, which are business vocabulary and so live here, not in a locale pack); a type: array property marks a repeating source (tables, repeats). validate cross-checks every template binding against it — unknown keys, undeclared display variants, missing data — and, when params are supplied, the params tree against the schema (required, types, ranges, enum).

Limitations

A {…} key outside [A-Za-z0-9_.] prints its own braces (interpolation_key_charset); a bindings: declaration is how such a key is reached.
A bindings: name outside the reference charset can never be referenced (invalid_binding_name), and the per-item registry is capped at 256 (too_many_bindings).
An inline format: { pattern } applies to date/datetime only; elsewhere the default form renders (format_pattern_ignored).
A currency with no display data falls back to the code itself (unknown_currency), and a unit key missing from the pack renders verbatim (unknown_unit).
Binding does no arithmetic. Totals, tax and rounding are computed by the host and bound as values — there is no expression syntax.

Diagnostics

Code	Meaning
`unknown_data_key`	binding key not in definitions (validate)
`unknown_format`	display variant not declared for the field (validate; registry names and the currency variants always pass)
`missing_data`	params has no value for a bound key (validate + layout); suppressed when a `placeholder` covers the binding
`not_an_array`	a table/repeat/list source key is not an array
`format_error`	value cannot render as the requested type (e.g. not a number); a `placeholder` suppresses it for a blank value but NOT for a present-but-invalid one
`unknown_format_variant`	a picked variant exists nowhere; the default form rendered (layout, deduped)
`unknown_currency`	a code without display data used the code itself as symbol/name (precision stayed correct)
`unknown_unit`	a semantic unit key missing from the pack rendered verbatim
`format_pattern_ignored`	an inline pattern on a non-dated type; the default form rendered
`interpolation_key_charset`	a `{…}` that looks like an intended key but uses characters outside `[A-Za-z0-9_.]`, so it prints its braces; declare a name for it
`unused_binding`	a `bindings:` declaration no string in the item references
`binding_shadows_key`	a declared name that also resolved at the ambient scope, redirected by the declaration (which wins)
`invalid_binding_name`	a declaration name outside the reference charset, so `{name}` could never reach it
`too_many_bindings`	more than 256 declarations on one item (advisory; all of them still work)

Capability keys: format.wareki, format.patterns.cldr, format.currency.variants, format.units.semantic, binding.placeholder, binding.declarations.

Data binding & formatting ​

The three binding forms ​

Blank-form placeholder ​

Where {…} resolves — not always params ​

Scopes ​

scope: — the escape back to the document ​

Named binding declarations ​

Params ​

Formats ​

Precedence (the effective format) ​

Pattern tokens (append-only inventory) ​

Era formatting (wareki) ​

Definitions (definitions.yml) ​

Limitations ​

Diagnostics ​

See also ​

Data binding & formatting

The three binding forms

Blank-form placeholder

Where `{…}` resolves — not always params

Scopes

`scope:` — the escape back to the document

Named binding declarations

Params

Formats

Precedence (the effective format)

Pattern tokens (append-only inventory)

Era formatting (wareki)

Definitions (`definitions.yml`)

Limitations

Diagnostics

See also