/MarkText2D displays a text (string) to a marked 3D position.
The marked position is the left end of the text.
/MarkText2D corresponds to class G4Text of GEANT4 with
its size given as world-coordinate size.
| Format | /MarkText2D x y z size x_offset y_offset string |
| (x, y, z) | marked 3D position (left end of string) |
| size | font size (3D unit) |
| x_offset | horizontal offset (3D unit) |
| y_offset | vertical offset (3D unit) |
| string | string to be displayed (Do not quote with ``''.) |