code: func (cs CallStack) TrimRuntime() CallStack {
  	for len(cs) > 0 && inGoroot(cs[len(cs)-1]) {
  		cs = cs[:len(cs)-1]
  	}
  	return cs
  }
docs: // TrimRuntime returns a slice of the CallStack with the topmost entries from
  // the go runtime removed. It considers any calls originating from unknown
  // files, files under GOROOT, or _testmain.go as part of the runtime.