Halliday & Matthiessen (2014: 517-8):
Something that is projected as a meaning is still a phenomenon of language – it is what was referred to above as a ‘metaphenomenon’; but it is presented at a different level – semantic, not lexicogrammatical. When something is projected as a meaning it has already been ‘processed’ by the linguistic system – it is a phenomenon of experience that has been construed as a meaning; but processed only once, not twice as in the case of a wording, where a phenomenon of experience is construed first as a meaning and then in turn as wording.