Less known std.gc

[bearophile]

The std.gc module of Phobos contains various things that I don't undertand:

void addRoot(void* p);
void removeRoot(void* p);
void addRange(void* pbot, void* ptop);
void removeRange(void* pbot);
void setTypeInfo(TypeInfo ti, void* p);
void* getGCHandle();
void setGCHandle(void* p);

Maybe you can point me to some more info about their usage and usefulness, or some code that uses them. (I think the docs of Phobos can gain some usage examples of those functions).

Bye and thank you,
bearophile