code: public DesignSpec addKeyline(float position, From from) {
          final Keyline keyline = new Keyline(position * mDensity, from);
          if (mKeylines.contains(keyline)) {
              return this;
          }
  
          mKeylines.add(keyline);
          return this;
      }
docs: Adds a keyline to the {@link DesignSpec}.