`element.getEmbeddedCells([opt])`

Return an array of all the embedded cells of an element. If all you need is `id`

's of all the embedded cells,
use `element.get('embeds')`

. If `opt.deep`

is `true`

, all the deeply embedded
cells will be returned. The order in which the cells are returned depends on the search algorithm used. By
default, Depth-first search (DFS) algorithm is used. If
`opt.breadthFirst`

is `true`

, the Breadth-first search algorithm will be used instead.