But the explicit marking of barriers is somewhat against the original appealing TAG idea that such constraints result from imposition of the CETM, according to which the position of the moved element and the verb it depends on must be in the same elementary structure, and from the further combination possibilities of this structure.
in local formalisms with an extended domain of locality such as TAG or tree-local and set-local MCTAG, such constraints result from the form of the elementary structures and from the locality of the derivation operation.