Passing arguments to MsiExec
The /v argument is used to pass command-line switches and values of public properties through to Msiexec.exe. For example:
Setup.exe /v:<MSIEXEC parameters>
Passing arguments to CMDLINE variable
The /z argument is used to pass data to the InstallScript system variable CMDLINE, as in:
Setup.exe /z"My Custom Data"
after which the variable CMDLINE would contain the string "My Custom Data".