code: public DesignSpec addSpacing(float position, float size, From from) {
          final Spacing spacing = new Spacing(position * mDensity, size * mDensity, from);
          if (mSpacings.contains(spacing)) {
              return this;
          }
  
          mSpacings.add(spacing);
          return this;
      }
docs: Adds a spacing mark to the {@link DesignSpec}.