gre.LEFT, gre.RIGHT, gre.CENTER, gre.TOP, gre.BOTTOM

gre.LEFT gre.RIGHT gre.CENTER gre.TOP gre.BOTTOM
                    

These are definitions for horizontal and vertical values and are a shorthand for the following numeric values representing alignment:

gre.LEFT1
gre.CENTER2
gre.RIGHT3
gre.TOP1
gre.BOTTOM3