explanation sendmessage summary numbers?

i've successfully used windows sendmessage slight assistance me several things calm editor, nonetheless any i am only duplicating pasting formula suggested others, i don't unequivocally know means. there always mysterious summary array parameter. i know formula numbers meant i indeed know duty (hopefully) small some-more self-sufficient future? thanks.

recent example:

using system.runtime.interopservices;

[dllimport("user32.dll")]
static extern int sendmessage(intptr hwnd, uint wmsg,uintptr wparam, intptr lparam);

sendmessage(myrichtextbox.handle, (uint)0x00b6, (uintptr)0, (intptr)(-1));