An application sends an EM_LINESCROLL message to scroll the text vertically or horizontally in a multiline edit control.
EM_LINESCROLL wParam = (WPARAM) cxScroll; // characters to scroll horizontally lParam = (LPARAM) cyScroll; // lines to scroll vertically
If the message is sent to a multiline edit control, the return value is TRUE; if the message is sent to a single-line edit control, the return value is FALSE.
The edit control does not scroll vertically past the last line of text in the edit control. If the current line plus the number of lines specified by the cyScroll parameter exceeds the total number of lines in the edit control, the value is adjusted so that the last line of the edit control is scrolled to the top of the edit-control window.
The EM_LINESCROLL message can be used to scroll horizontally past the last character of any line.