Grid gadgets layout their children in a rectangular grid. The grid is represented as a sequence of sequences of gadgets. Every child sequence is a row of gadgets. Every row must have an equal number of gadgets in it.

Creating grids from a fixed set of gadgets:
<grid> ( children -- grid )

Managing children:
grid-add ( grid child pair -- grid )

grid-remove ( grid pair -- grid )

grid-child ( grid pair -- gadget )

Grid lines:
Grid lines