When reading several dtx files in order to write my own, I saw the command
\SB@... in front of several other commands. What does it mean? I could not find reliable sources as explanation.
It is not in front of the command it is part of the command, in packages
@ is a letter so
\SB@foobar is just the command with name
\SB@foobar package authors often use such a naming scheme to avoid clashes with other packages.
In this case the
songs package author has used this naming scheme
\SB@star could have been called
@ has no special role here other than for example all
longtable package internals are called
\LT@... so the chance of two packages clashing is reduced.