@type kind() :: :button | :text | :choice | :signature | :unknown

The field's type, as declared by the PDF's /FT entry.

• :button — push buttons, check boxes and radio groups.
• :text — free-text entry.
• :choice — list boxes and combo boxes.
• :signature — a digital signature field.
• :unknown — the field declares no recognized type.

@type value() ::
  {:text, String.t()}
  | {:boolean, boolean()}
  | {:name, String.t()}
  | {:array, [String.t()]}
  | nil

A field's value, tagged by the shape the PDF stores it in.

The tag follows the underlying PDF object rather than the field's kind/0, so match on the tag rather than inferring it from the kind:

• {:text, value} — a text string. The usual shape for a :text field, and for a :choice field with one selection.
• {:boolean, value} — a true/false toggle.
• {:name, value} — a PDF name, without its leading slash. How a check box or radio group reports its state, typically "Off" when unset and the on-state's name when set.
• {:array, values} — several strings, e.g. a multi-select :choice field.
• nil — the field carries no value.

PdfElixide.Form.set_value/3 accepts exactly these shapes, so a value read from one field can be written to another unchanged. Anything else — a bare string, an unrecognized tag — raises ArgumentError.