PSSE 30 Test System: it builds, but with errors logged

When I try to do build_system(PSSEParsingTestSystems, "PSSE 30 Test System"; force_build=true), having PSY and PSB both dev'ed to their psy5 branches, I get the following errrors:

┌ Error: Three-winding transformer from PowerFlowData inputs not implemented. Data will be ignored
└ @ PowerSystems ~/Documents/julia/Sienna/psy5/PowerSystems.jl/src/parsers/powerflowdata_data.jl:568
┌ Error: SwitchedShunts parsing from PSS/e v30 files not implemented. Data will be ignored
└ @ PowerSystems ~/Documents/julia/Sienna/psy5/PowerSystems.jl/src/parsers/powerflowdata_data.jl:732
┌ Error: TwoTerminalDCLines parsing from PSS/e v30 files not implemented. Data will be ignored
└ @ PowerSystems ~/Documents/julia/Sienna/psy5/PowerSystems.jl/src/parsers/powerflowdata_data.jl:773
┌ Error: MultiTerminalDCLines parsing from PSS/e files v30 not implemented. Data will be ignored
└ @ PowerSystems ~/Documents/julia/Sienna/psy5/PowerSystems.jl/src/parsers/powerflowdata_data.jl:806
┌ Error: VSCDCLines parsing from PSS/e files not implemented. Data will be ignored
└ @ PowerSystems ~/Documents/julia/Sienna/psy5/PowerSystems.jl/src/parsers/powerflowdata_data.jl:795
┌ Error: Model doesn't contain a slack bus
└ @ PowerSystems ~/Documents/julia/Sienna/psy5/PowerSystems.jl/src/utils/IO/system_checks.jl:27

The last error I confirm: see https://github.com/NREL-Sienna/PowerSystemsTestData/blob/99e38b7b2366a7f60357139ad13e50914f44d0ec/psse_raw/synthetic_data_v30.raw#L4C1-L6C89 The 4th entry is bus type: all are 1's, meaning 4 load buses.

However, I'm not sure how to handle the other ones: remove the unsupported features from the file? Or leave it as-is?

Start with the build_system call for "PSSE 30 Test System" and inspect synthetic_data_v30.raw, especially the bus records linked in the issue. Read the parser locations in powerflowdata_data.jl and the slack-bus check in system_checks.jl, then determine and document the expected test-data handling for each logged unsupported feature and the all-load-bus condition.