    element.toFront([opt])

Move the element so it is on top of all other cells (element/links). If `opt.deep` is `true`, all the embedded cells of this element will get higher `z` index than that of this element in a Breadth-first search (BFS) fashion. This is especially useful in hierarchical diagrams where if you want to send an element to the front, you don't want its children (embedded cells) to be hidden behind that element.

All elements have a `z` property defining their z-level in the graph. This `z` property can even be set directly by `element.set('z', 123)`. This change will be automatically handled by the `joint.dia.Paper` object associated with the `joint.dia.Graph` object this element is part of and all the SVG elements will get resorted so that their position in the DOM reflects the `z` level.