text: // eslint-disable no-unused-vars
  // ValueDef is { value: xxx }
  // PositionFieldDef is { field: 'fieldName', scale: xxx, axis: xxx }
  export function isValueDef(a){return a&&"value"in a}export function isNonValueDef(a){return a&&!("value"in a)}export function isFieldDef(a){return a&&"field"in a&&!!a.field}export function isTypedFieldDef(a){return isFieldDef(a)&&"type"in a&&!!a.type}export function isScaleFieldDef(a){return a&&("scale"in a||"sort"in a)}export function isMarkPropFieldDef(a){return a&&"legend"in a}export function isPositionFieldDef(a){return a&&("axis"in a||"stack"in a||"impute"in a)}