# SB@ in dtx and sty files

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
 \def\SB@star...

so \SB@star could have been called \zzzstar the @ 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.