center centers the children of an object with respect to the first child along selected dimensions.

In example below, there are three cylinders with varying heights and radiuses. Initially, they all meet at the origin (0,0,0).

When no axis was given (i.e., t="center"), centering is done in all dimensions. When some axes are specified (i.e., t="center xy"), centering is done in those axes. For instance, center xy centers the three cylinders in x and y axes with respect to the first child, which is the pink disk.