Specifies the available values for PDFStandardLayoutAttribute.setBlockAlign.
After edge of the last child's allocation rectangle aligned with that of the table cell's content rectangle.
Before edge of the first child's allocation rectangle aligned with that of the table cell's content rectangle.
Children aligned with both the before and after edges of the table cell's content rectangle. The first child shall be placed as described for BEFORE and the last child as described for AFTER, with equal spacing between the children. If there is only one child, it shall be aligned with the before edge only, as for BEFORE.
Children centred within the table cell. The distance between the before edge of the first child's allocation rectangle and that of the table cell's content rectangle shall be the same as the distance between the after edge of the last child's allocation rectangle and that of the table cell's content rectangle.