Check function names (I inferred from the code, there might be better scientific names, maybe )
'_append_target_sites' where I set the 'spacing' key for given distances (hope it makes sense).
Tests: I tested with the newly implemented test 'trellis_test_from_properties' which is a modification of the original 'trellis_test' (which does not break). I did not run all other tests though.
TBD: