code: function mountTo(root, tagName, opts) {
    var tag = __tagImpl[tagName],
      // cache the inner HTML to fix #855
      innerHTML = root._innerHTML = root._innerHTML || root.innerHTML
  
    // clear the inner html
    root.innerHTML = ''
  
    if (tag && root) tag = new Tag(tag, { root: root, opts: opts }, innerHTML)
  
    if (tag && tag.mount) {
      tag.mount()
      // add this tag to the virtualDom variable
      if (!contains(__virtualDom, tag)) __virtualDom.push(tag)
    }
  
    return tag
  }
docs: Mount a tag creating new Tag instance
  @param   { Object } root - dom node where the tag will be mounted
  @param   { String } tagName - name of the riot tag we want to mount
  @param   { Object } opts - options to pass to the Tag instance
  @returns { Tag } a new Tag instance