EFI_ACPI_5_0_WATCHDOG_RESOURCE_TABLE_SIGNATURE

Undocumented in source but is binding to C. You might be able to learn more by searching the web for its name.
extern (C)
enum EFI_ACPI_5_0_WATCHDOG_RESOURCE_TABLE_SIGNATURE = SIGNATURE_32('W', 'D', 'R', 'T');

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