This type of analysis into constituents is often known as BRACKETING, and the costituent structure can be shown equally well by the use of brackets […] Whichever device we use, brackets or trees, the notation shows what goes together with what; and in what order, beginning with the units that are most closely bonded (letters bonded into words) and working up through the hierarchy of graphic units until we reach whatever is the highest one to be identified.
- Halliday (1985), a pag.3

Bracketing is a way of showing what goes with what: in what logical (as opposed to sequential) order the elements of a linguistic structure are combined. It says nothing about either the nature or the function of the elements themselves.
- Halliday (1985), a pag.27