More blank tile information

[Asuna Yuuki Nagato]

The Blank Tile Information msgbox (accessible from the Select Tile window's right click context menu) seems to either say:

Tile is not blank.

or

Tile is blank.

followed by a 2x2 matrix of X's or -'s, but doesn't say what this matrix represents.

[Asuna Yuuki Nagato]

This msgbox is created by show_blank_tile in zq_tiles.cpp