BGMSET is not a command in SmileBasic V1.
BGMSET is a command for specifying "songs" that can be played with the
BGMSET has at between two and ten parameters (inclusive). The first is a numeric parameter, between 128 and 255 inclusive, and defines the "song number". The remaining parameters are strings, and are concatenated and interpreted as MML.
BGMSET 128,"EDCDEEE" will set song 128 to the first few notes of Mary Had A Little Lamb, and you can hear these notes by using
See also BGMSETD (Command).
No information on SmileBasic V3.