The Microsoft Universal Printer Driver (Unidrv) and Microsoft PostScript Printer Driver (Pscript5) core printer drivers on Windows Vista provide the means for plug-ins to implement print ticket support. Because Unidrv and Pscript5 both support loading multiple plug-ins for a single driver, each plug-in is able to provide its own provider implementation. The driver vendor is responsible for ensuring that each of the OEM plug-in provider implementations works correctly with the others. Not all of the plug-ins in a printer driver need to support the provider interface. However, the versions of the print ticket schema that are supported by the core driver are a subset of the versions that are supported by the core driver and all of the available plug-in providers. Because calls into the plug-in provider are driven by the application, the plug-in provider must be implemented in a thread-safe manner.