EN_VSCROLL
The EN_VSCROLL notification message is sent when the user clicks an edit control's vertical scroll bar. The control's parent window receives this notification message through a WM_COMMAND message. The parent window is notified before the screen is updated.
wParam
Specifies the identifier of the edit control.
lParam
Specifies the handle of the edit control in the low-order word, and specifies the EN_VSCROLL notification message in the high-order word.