Halliday (2008: 67):
[…] you can, as expected, network through the grammar into the lexis; but what you end up with are not lexical items but lexical features. The lexical item will appear, but it will appear as a conjunct realisation of a number of these terminal features. The features are thus components of the lexical items, but the description differs from a usual componential analysis in two important respects. In the first place, the components are systemic: they are organised in sets of systemic options; and in the second place, more significantly, they are derived by ordered steps in delicacy all the way from the primary grammatical categories.