docs: function prepend(tagName) {
    //the same as append, but inserting the element before the first element in the container
    const elements = [];
  
    this.each(function() {
      const document = this.ownerDocument;
      const element = document.createElement(tagName);
      this.insertBefore(element, this.firstChild);
      elements.push(element);
    });
  
    return selectAll(elements);
  }