A zoomable value which specifies how much to offset the line from the original line position, parallel to this original position. line-offset is specified in offset pixels. line-offset-sides property specifies in which direction(s) to offset the line.
define line-color : red line-opacity : 0.8 line-offset : 14:0;15:3;16:5 line-offset-sides : left draw : line
draws the line offset 5 pixels to the left (on zoom level 16 and higher), like in this example:
You should be careful when specifying offsets - a value too large can produce unwanted artifacts: