Sourcepos not defined for inline elements

Trying to parse this file with commonmark as follows:

    const parser = new commonmark.Parser({ sourcepos: true });
    const result = parser.parse(source);

Where source is:

# API name

# Group Users

## User [/users/{id}]

+ Parameters
    + id: 23 (enum[number], optional) - Database ID

        Additional description

        + Default: 1

        + Members
            + 37 - Testing value
            + 1
            + 23

### Retrieve User [GET]

+ Response 200 (application/json)

        {}

The node with Additional description literal ends up having undefined sourcepos. According to the description, sourcepos property is listed under "The following public properties are defined".

The resulting node is:

Node {
  _type: 'text',
  _parent:
   Node {
     _type: 'paragraph',
     _parent:
      Node {
        _type: 'item',
        _parent: [Object],
        _firstChild: [Object],
        _lastChild: [Object],
        _prev: null,
        _next: null,
        _sourcepos: [Array],
        _lastLineBlank: true,
        _open: false,
        _string_content: '',
        _literal: null,
        _listData: [Object],
        _info: null,
        _destination: null,
        _title: null,
        _isFenced: false,
        _fenceChar: null,
        _fenceLength: 0,
        _fenceOffset: null,
        _level: null,
        _onEnter: null,
        _onExit: null },
     _firstChild: [Circular],
     _lastChild: [Circular],
     _prev:
      Node {
        _type: 'paragraph',
        _parent: [Object],
        _firstChild: [Object],
        _lastChild: [Object],
        _prev: null,
        _next: [Circular],
        _sourcepos: [Array],
        _lastLineBlank: true,
        _open: false,
        _string_content: null,
        _literal: null,
        _listData: {},
        _info: null,
        _destination: null,
        _title: null,
        _isFenced: false,
        _fenceChar: null,
        _fenceLength: 0,
        _fenceOffset: null,
        _level: null,
        _onEnter: null,
        _onExit: null },
     _next:
      Node {
        _type: 'list',
        _parent: [Object],
        _firstChild: [Object],
        _lastChild: [Object],
        _prev: [Circular],
        _next: null,
        _sourcepos: [Array],
        _lastLineBlank: true,
        _open: false,
        _string_content: '',
        _literal: null,
        _listData: [Object],
        _info: null,
        _destination: null,
        _title: null,
        _isFenced: false,
        _fenceChar: null,
        _fenceLength: 0,
        _fenceOffset: null,
        _level: null,
        _onEnter: null,
        _onExit: null },
     _sourcepos: [ [Array], [Array] ],
     _lastLineBlank: true,
     _open: false,
     _string_content: null,
     _literal: null,
     _listData: {},
     _info: null,
     _destination: null,
     _title: null,
     _isFenced: false,
     _fenceChar: null,
     _fenceLength: 0,
     _fenceOffset: null,
     _level: null,
     _onEnter: null,
     _onExit: null },
  _firstChild: null,
  _lastChild: null,
  _prev: null,
  _next: null,

  _sourcepos: undefined,

  _lastLineBlank: false,
  _open: true,
  _string_content: null,

  _literal: 'Additional description',

  _listData: {},
  _info: null,
  _destination: null,
  _title: null,
  _isFenced: false,
  _fenceChar: null,
  _fenceLength: 0,
  _fenceOffset: null,
  _level: null,
  _onEnter: null,
  _onExit: null }

Expected: node.sourcepos contains an array
Actual: node.sourcepos is undefined

Start by reproducing the provided parser example with sourcepos enabled and inspect how the inline text node for “Additional description” is created. Trace the sourcepos handling for that node and add a regression test; done means node.sourcepos is an array containing the expected position.