public StringProperty unitProperty() {
        if (null == unit) {
            unit  = new StringPropertyBase(_unit) {
                @Override protected void invalidated() { fireTileEvent(VISIBILITY_EVENT); }
                @Override public Object getBean() { return Tile.this; }
                @Override public String getName() { return "unit"; }
            };
            _unit = null;
        }
        return unit;
    }
Sets the unit of the tile. This unit will usually only be
visible if it is not empty.

@param UNIT
src/main/java/eu/hansolo/tilesfx/Tile.java