Halliday & Matthiessen (2014: 380):
Often the participle is itself further modified, as in a fast-moving train, a hard-boiled egg. The resulting compound may embody any one of a number of different experiential relations, e.g. well-meaning, habit-forming, fund-raising, right-angled, fruit-flavoured, pear-shaped, architect-designed, simple-minded, bottled-nosed, iron-fisted, two-edged.
What is happening here is that some part of the experiential structure of a clause is being downgraded to function as Epithet or Classifier; it is a reduced form of a non-finite clause and hence agnate to a (finite or non-finite) Qualifier.