Horizontal position of the element's "origin" relative to the "origin" of an enclosing container element. The origin for most items is their top-left corner but for unALIGNed TEXT it is the leftmost point of the first character's baseline.
The default UNIT is 1/600 inch, so:
would set the horizontal position to 1" inside the container's left boundary. If a 'unit' value is appended to the offset value, the current unit value is overridden for that item, e.g.