code: function UpChildren(elt, children) {
    var f = C(function _UpChildren(children) {
  
      filter.call(elt.childNodes, child => children.indexOf(child) === -1)
        .forEach(removeChild, elt);
  
      children
        .filter(Boolean)
        .map(c => typeof c.valueOf() === 'string' ? T(c) : c)
        .forEach(appendChild, elt);
    });
  
    // Permit any combination of single nodes and arrays as arguments.
    f(Array.isArray(children) ? children : [children]);
    return elt;
  }
docs: ## upChildren
  
  Specify the children of an HTML element.
  As the input array changes, the element's children are added and removed.
  
  @param {HTMLElement} elt element to add children to
  @param {Node[]} children array of nodes to add as children