code: function makeTextContent(textContent) {
    // NOTE: Null values reduce hidden classes.
    return {
      type: 'TEXT_CONTENT',
      content: textContent,
      fromIndex: null,
      fromNode: null,
      toIndex: null,
      afterNode: null
    };
  }
docs: Make an update for setting the text content.
  
  @param {string} textContent Text content to set.
  @private