Complex sentence: It may refer to encasing the head in a bondage hood, or a head harness with blindfold and gag, possibly with a wide, stiff collar round the neck to restrict movement of the head.
Split into simpler sentences: It may refer to encasing the head in a bondage hood, or a head harness. The encasement may include or be accentuated with a wide, stiff collar round the neck to restrict movement of the head.