How to use the mobiledoc-kit/utils/dom-utils.isTextNode function in mobiledoc-kit

parse(element) {
    if (this._isSkippable(element)) {
      return [];
    }
    this.sections = [];
    this.state = {};

    this._updateStateFromElement(element);

    let finished = false;

    // top-level text nodes will be run through parseNode later so avoid running
    // the node through parserPlugins twice
    if (!isTextNode(element)) {
      finished = this.runPlugins(element);
    }

    if (!finished) {
      let childNodes = isTextNode(element) ? [element] : element.childNodes;

      forEach(childNodes, el => {
        this.parseNode(el);
      });
    }

    this._closeCurrentSection();

    return this.sections;
  }

parseNode(node) {
    if (!this.state.section) {
      this._updateStateFromElement(node);
    }

    let nodeFinished = this.runPlugins(node);
    if (nodeFinished) {
      return;
    }

    // handle closing the current section and starting a new one if we hit a
    // new-section-creating element.
    if (this.state.section && !isTextNode(node) && node.tagName) {
      let tagName = normalizeTagName(node.tagName);
      let isListSection = contains(VALID_LIST_SECTION_TAGNAMES, tagName);
      let isListItem = contains(VALID_LIST_ITEM_TAGNAMES, tagName);
      let isMarkupSection = contains(VALID_MARKUP_SECTION_TAGNAMES, tagName);
      let isNestedListSection = isListSection && this.state.section.isListItem;
      let lastSection = this.sections[this.sections.length - 1];

      // we can hit a list item after parsing a nested list, when that happens
      // and the lists are of different types we need to make sure we switch
      // the list type back
      if (isListItem && lastSection && lastSection.isListSection) {
        let parentElement = node.parentElement;
        let parentElementTagName = normalizeTagName(parentElement.tagName);
        if (parentElementTagName !== lastSection.tagName) {
          this._closeCurrentSection();
          this._updateStateFromElement(parentElement);

}
    this.sections = [];
    this.state = {};

    this._updateStateFromElement(element);

    let finished = false;

    // top-level text nodes will be run through parseNode later so avoid running
    // the node through parserPlugins twice
    if (!isTextNode(element)) {
      finished = this.runPlugins(element);
    }

    if (!finished) {
      let childNodes = isTextNode(element) ? [element] : element.childNodes;

      forEach(childNodes, el => {
        this.parseNode(el);
      });
    }

    this._closeCurrentSection();

    return this.sections;
  }

_getSectionDetails(element) {
    let sectionType,
        tagName,
        inferredTagName = false;
    if (isTextNode(element)) {
      tagName = DEFAULT_TAG_NAME;
      sectionType = MARKUP_SECTION_TYPE;
      inferredTagName = true;
    } else {
      tagName = normalizeTagName(element.tagName);

      if (contains(VALID_LIST_SECTION_TAGNAMES, tagName)) {
        sectionType = LIST_SECTION_TYPE;
      } else if (contains(VALID_LIST_ITEM_TAGNAMES, tagName)) {
        sectionType = LIST_ITEM_TYPE;
      } else if (contains(VALID_MARKUP_SECTION_TAGNAMES, tagName)) {
        sectionType = MARKUP_SECTION_TYPE;
      } else {
        sectionType = MARKUP_SECTION_TYPE;
        tagName = DEFAULT_TAG_NAME;
        inferredTagName = true;

_markupsFromElement(element) {
    let { builder } = this;
    let markups = [];
    if (isTextNode(element)) {
      return markups;
    }

    const tagName = normalizeTagName(element.tagName);
    if (this._isValidMarkupForElement(tagName, element)) {
      markups.push(builder.createMarkup(tagName, getAttributes(element)));
    }

    this._markupsFromElementStyle(element).forEach(
      markup => markups.push(markup)
    );

    return markups;
  }

_markupsFromElement(element) {
    let { builder } = this;
    let markups = [];
    if (isTextNode(element)) {
      return markups;
    }

    const tagName = normalizeTagName(element.tagName);
    if (this._isValidMarkupForElement(tagName, element)) {
      markups.push(builder.createMarkup(tagName, getAttributes(element)));
    }

    this._markupsFromElementStyle(element).forEach(
      markup => markups.push(markup)
    );

    return markups;
  }

function findOffsetInNode(node, coords) {
  let closest, dyClosest = 1e8, coordsClosest, offset = 0;
  for (let child = node.firstChild; child; child = child.nextSibling) {
    let rects;
    if (isElementNode(child)) {
      rects = child.getClientRects();
    } else if (isTextNode(child)) {
      rects = textNodeRects(child);
    } else {
      continue;
    }

    for (let i = 0; i < rects.length; i++) {
      let rect = rects[i];
      if (rect.left <= coords.left && rect.right >= coords.left) {
        let dy = rect.top > coords.top ? rect.top - coords.top
            : rect.bottom < coords.top ? coords.top - rect.bottom : 0;
        if (dy < dyClosest) {
          closest = child;
          dyClosest = dy;
          coordsClosest = dy ? {left: coords.left, top: rect.top} : coords;
          if (isElementNode(child) && !child.firstChild) {
            offset = i + (coords.left >= (rect.left + rect.right) / 2 ? 1 : 0);

_getSectionDetails(element) {
    let sectionType,
        tagName,
        inferredTagName = false;
    if (isTextNode(element)) {
      tagName = DEFAULT_TAG_NAME;
      sectionType = MARKUP_SECTION_TYPE;
      inferredTagName = true;
    } else {
      tagName = normalizeTagName(element.tagName);

      if (contains(VALID_LIST_SECTION_TAGNAMES, tagName)) {
        sectionType = LIST_SECTION_TYPE;
      } else if (contains(VALID_LIST_ITEM_TAGNAMES, tagName)) {
        sectionType = LIST_ITEM_TYPE;
      } else if (contains(VALID_MARKUP_SECTION_TAGNAMES, tagName)) {
        sectionType = MARKUP_SECTION_TYPE;
      } else {
        sectionType = MARKUP_SECTION_TYPE;
        tagName = DEFAULT_TAG_NAME;
        inferredTagName = true;