Halliday & Matthiessen (1999: 209-10):
Qualities can be distinguished according to the transphenomenal types of projection and expansion. Qualities of projection and qualities of expansion differ in a number of respects. Most fundamentally, they differ in their patterns of agnation.
Qualities of projection are agnate with processes in figures of sensing; for example, happy in the happy child (or the child is happy) is agnate with rejoice in the child rejoices.
In contrast, qualities of expansion display patterns of agnation within figures of being & having, with variation according to subtype.
This fundamental difference explains other differences; for example, qualities of projection tend to occur in agnate pairs of the 'like' and 'please' type that we find with figures of sensing (e.g. afraid/scary, suspicious/suspect, bored/boring), whereas qualities of expansion do not.