Xerox Paris, a document system Support & Software User Guide

If the Visible box is checked, the grid displays as a dotted
array.

The grid can be made visible whether active or not as a
visual aid to the positioning of elements.

If the Active box is checked, an element being placed will
automatically align to the nearest grid-line, ensuring
consistent alignment and positioning of elements.

The Half option is only effective if the Active box is checked.

Selecting the Half checkbox turns on grid points half-way
between the horizontal and vertical units. This assists in more
exact positioning of elements. The half-way points do not
display.