Specifies how much to offset the text on its vertical axis. This property is used by the text symbol and is specified as a zoomable value. The value can be specified either in pixels or as a percentage of the font-size. Positive values move the text down on the map while negative values move the text up.
Examples:
define text-offset-vertical : 24 draw : text
draws the text at 24 pixels down from the original position.
define font-size : 8 text-offset-vertical : 200% draw : text
draws the text at 16 pixels down from the original position.
