In the latter case, it will be placed in the center of a cell. Cactus supports three kind of staggering per dimension. M no staggering, default. C centre staggering. P full staggerd.
P refers to plus.
For multi dimensional gridfunctions you concatenate the code characters in xyz order. In picture xy we show four different staggerings of a two dimensional grid functions. The solid black grid circles show the default location of the grid functions at the intersections of the grid lines. Note that the staggering of gridfunctions does change its index.