Some parameter values need the whole song or at least the unit to give accurate hint what the parameter means. For example: send needs to know the entire song to know what the target unit refers to.
assume songs code it as 1 always; implementations are free to change this during compilation, but this should be a compile time flag / optimization; not a concern of song.
The global pattern table is constructed only during compilation. At this point, we can do also all sorts of optimizations / changes e.g. remove unnecessary releases and reuse patterns if there's a pattern already that could be used.
Play depends on bridge and compile on compiler package. Before, the compiler depended on bridge, but we could not use the compiler to build the library, as the bridge depends on the library. Also, play can now start having slightly more options e.g. wav out etc.
