Halliday & Matthiessen (2014: 155):
The typical order of elements in the Residue is: Predicator ^ Complement(s) ^ Adjunct(s) … But … an Adjunct or Complement may occur thematically, either as a WH- element in an interrogative clause or as marked Theme in a declarative clause. This does not mean that it becomes part of the Mood element; it is still within the Residue. As a result, therefore, the Residue is split into two parts; it becomes discontinuous.