The spec for this action:
https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf#G11.2111850
An example of a form using this action:
https://www2.illinois.gov/rev/forms/reg/Documents/reg-1-mr.pdf
nIdx = Array.isArray(this._currentValueIndices)
        ? this._currentValueIndices[0]
        : this._currentValueIndices;
      nIdx = nIdx || 0;
    }
    if (nIdx < 0 || nIdx >= this.numItems) {
      nIdx = this.numItems - 1;
    }
    this._items.splice(nIdx, 1);
    if (Array.isArray(this._currentValueIndices)) {
      let index = this._currentValueIndices.findIndex(i => i >= nIdx);
      if (index !== -1) {
        if (this._currentValueIndices[index] === nIdx) {
          this._currentValueIndices.splice(index, 1);
        }
        for (const ii = this._currentValueIndices.length; index < ii; index++) {
          --this._currentValueIndices[index];
        }
      }
    } else {
      if (this._currentValueIndices === nIdx) {
        this._currentValueIndices = this.numItems > 0 ? 0 : -1;
      } else if (this._currentValueIndices > nIdx) {
        --this._currentValueIndices;
      }
    }
    this._send({ id: this._id, remove: nIdx });
  }
  getItemAt(nIdx = -1, bExportValue = false) {