code: function (sector, level, row, column, cacheKey) {
              if (!cacheKey || (cacheKey.length < 1)) {
                  throw new ArgumentError(
                      Logger.logMessage(Logger.LEVEL_SEVERE, "FramebufferTile", "constructor",
                          "The specified cache name is null, undefined or zero length."));
              }
  
              TextureTile.call(this, sector, level, row, column); // args are checked in the superclass' constructor
  
              // Assign the cacheKey as the gpuCacheKey (inherited from TextureTile).
              this.gpuCacheKey = cacheKey;
  
              // Internal. Intentionally not documented.
              this.textureTransform = Matrix.fromIdentity().setToUnitYFlip();
  
              // Internal. Intentionally not documented.
              this.mustClear = true;
          }
docs: Constructs a framebuffer tile.
  @alias FramebufferTile
  @constructor
  @augments TextureTile
  @classdesc Represents a WebGL framebuffer applied to a portion of a globe's terrain. The framebuffer's width
  and height in pixels are equal to this tile's [tileWidth]{@link FramebufferTile#tileWidth} and
  [tileHeight]{@link FramebufferTile#tileHeight}, respectively. The framebuffer can be made active by calling
  [bindFramebuffer]{@link FramebufferTile#bindFramebuffer}. Color fragments written to this
  tile's framebuffer can then be drawn on the terrain surface using a
  [SurfaceTileRenderer]{@link SurfaceTileRenderer}.
  <p>
  This class is meant to be used internally. Applications typically do not interact with this class.
  @param {Sector} sector The sector this tile covers.
  @param {Level} level The level this tile is associated with.
  @param {Number} row This tile's row in the associated level.
  @param {Number} column This tile's column in the associated level.
  @param {String} cacheKey A string uniquely identifying this tile relative to other tiles.
  @throws {ArgumentError} If the specified sector or level is null or undefined, the row or column arguments
  are less than zero, or the cache name is null, undefined or empty.