Martin (1992: 101):
Relevance Phoricity –
CIRCUMSTANCE OF MANNER & EXTENT
[3:10] The boy ran quickly for a few yards;
but his dog ran farther and faster.
[3:11] The frog ran away
so the boy went to find it.
[3:12] The boy felt worried
and his dog did too.
 To be clear, "relevance phoricity" is Martin's rebranding of Halliday's comparative reference. Halliday & Matthiessen (2014: 632-3 ):
Whereas personals and demonstratives, when used anaphorically, set up a relation of co-reference, whereby the same entity is referred to over again, comparatives set up a relation of contrast. In comparative reference, the reference item still signals ‘you know which’; not because the same entity is being referred to over again but rather because there is a frame of reference — something by reference to which what I am now talking about is the same or different, like or unlike, equal or unequal, more or less.
 Here Martin confuses a structural hypotactic relation of cause between clauses (logical metafunction) with a non-structural relation of cohesive conjunction (textual metafunction), and misinterprets the conjunctive Adjunct (so) as a comparative reference item, with the preceding clause as its referent.
 Here Martin misinterprets a conjunctive Adjunct (too) — itself misunderstood as a marker of continuity, see Halliday & Matthiessen (2014: 603-5) — as a comparative reference item, with the preceding clause in the nexus of paratactic addition as its referent. Halliday & Matthiessen (2014: 472)
Paratactic additions are often accompanied by cohesive expressions serving as conjunctive Adjuncts such as too, in addition, also, moreover, on the other hand.