in short:
- you use only HD elements and play HD = HD elements are used
- you use only HD elements and play SD = default elements are used
- you use only SD elements and play SD = SD elements are used
- you use only SD elements and play HD = SD elements are used
- you use SD and HD elements and play HD = HD elements are used and missing stuff is taken from SD stuff instead of default
- you use SD and HD elements and play SD = SD elements are used and HD elements ignored.