This sample project was created to depict GVim bug
when it is started with --windowid switch.
For example, your parent window handle is 0x50830
and when you start gvim as following
gvim --windowid 0x50830
it must run inside your parent window covering its whole client area. But in fact, on Windows, when your run it in such manner you'll get weird gray gaps around gvim editing area...
But when you resize the container window, dragging window frame with mouse, you'll see that gvim adapts to client area... With some integral steps however.