What is the use of : m_windowAlloc.alloc();

[meiry]

hey ,
I can see in https://github.com/bkaradzic/bgfx/blob/master/examples/common/entry/entry_sdl.cpp#L499
that is using m_windowAlloc.alloc(); itried to find documention on this allocation of handlers without success .
in my application when working with SDL do i have to do this allocation ?
what it used to any way ? where i can read about it
Thanks