Halliday & Matthiessen (1999: 108):
We have suggested that the relation of projection sets up one figure on a different plane of reality — we refer to this as the second-order or semiotic level. This second-order level of reality is the content plane of a semiotic system. That is to say, the projected figure is projected in the form of ‘content’. We have seen that the content plane is stratified into two levels — semantics (the level of meanings) and lexicogrammar (the level of wordings). Consequently, we would expect projections to be located at either or both of these levels, and this is indeed what happens: a projected figure is either a meaning or a wording. […] We will refer to these [i.e. meaning and wording] in the context of projection as ideas and locutions.