The element is edited in slide mode (not yet implemented): moving the element replacing or consuming content on each end.
When acting on the element as a whole, this will MOVE the element, and TRIM any neighbours on either side. A neighbour is defined in the same way as in ROLL, but they may be on either side of the edited elements. Elements at the end with be START-TRIMMED to the new end position of the edited element. Elements at the start will be END-TRIMMED to the new start position of the edited element. Acting on the start or end of the element ( START and END) is not defined. The element can not shift layers under this mode.