RtlIsCloudFilesPlaceholder - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTRTL_H
// Cloud Filters
#if (PHNT_VERSION >= PHNT_REDSTONE3)

// msdn
NTSYSAPI
BOOLEAN
NTAPI
RtlIsCloudFilesPlaceholder(
    _In_ ULONG FileAttributes,
    _In_ ULONG ReparseTag
    );

#endif
#endif

View code on GitHub

This function is documented in Windows Driver Kit.