AxFieldValue

type AxFieldValue = 
  | string
  | string[]
  | number
  | boolean
  | object
  | null
  | undefined
  | {
  data: string;
  mimeType: string;
}
  | object[]
  | {
  data: string;
  format?: "wav";
}
  | object[];

Defined in: https://github.com/ax-llm/ax/blob/9a5a7060a48f9eef46efc680b0cdf6b42bff5df2/src/ax/dsp/types.ts#L14