ternativeId);
    });
    this.$container.appendChild(this.$displayLink);
    this.$outer.appendChild(this.$container);
    document.body.appendChild(this.$outer);
  },

  activate(el) {
    clearTimeout(this.deactiveTimeout);
    Toolbox.deactivate();
    this.$alternativeId = el.id;
    let numSdos = Object.keys(sdoMap[this.$alternativeId] || {}).length;
    this.$displayLink.textContent = 'Syntax-Directed Operations (' + numSdos + ')';
    this.$outer.classList.add('active');
    let top = el.offsetTop -