BootFlags in the LOADER_PARAMETER_EXTENSION

Somewhere among the 1607, 1703 and 1709 releases of Windows 10, Microsoft formalised that the BootFlags member of the LOADER_PARAMETER_EXTENSION is interpreted in bits. The C-language definition from NTOSP.H that Microsoft published in the Windows Driver Kit (WDK) for Windows 10 in the original and 1511 releases has just the integral BootFlags. Type information that public symbol files show for the structure in 1803 and higher present BootFlags in union with a set of ULONGLONG bit fields:

Mask Definition Versions
0x00000000`00000001
ULONGLONG DbgMenuOsSelection : 1;
1803 and higher;
no earlier than 1607
0x00000000`00000002
ULONGLONG DbgHiberBoot : 1;
1803 and higher;
no earlier than 1607
0x00000000`00000004
ULONGLONG DbgSoftRestart : 1;
1803 and higher;
no earlier than 1607
0x00000000`00000008
ULONGLONG DbgMeasuredLaunch : 1;
1809 and higher