Halliday & Matthiessen (1999: 212):
Qualities of elaboration, subtype identity are not inherent properties, but rather are comparative. Thus the standard of comparison can always be construed: their car is the same/similar/different : their car is the same as/similar to/different from ours; and they are agnate with processes: their car is/resembles/differs from ours. The line between elaboration: identity and enhancement: manner, comparison is a fuzzy one; and processual agnates such as their car resembles ours are within the domain of enhancement.