How does Password Revealer work?

Here's the main code in C:

BOOL CALLBACK EnumWindowsProc(HWND hwnd,LPARAM lParam);
BOOL CALLBACK EnumWindowsProc2(HWND hwnd,LPARAM lParam);

LRESULT CALLBACK MainWndProc(HWND hWndMain,UINT Msg,UINT wParam,LONG lParam)
{
    switch(Msg) {
        case WM_COMMAND:                  
            if(HIWORD(wParam)==BN_CLICKED) 
                EnumWindows(EnumWindowsProc,0); // call every main window
                break;
        case WM_DESTROY:
             PostQuitMessage(0);
             return 0L;
    }
    return DefWindowProc(hWndMain,Msg,wParam,lParam);
}          

BOOL CALLBACK EnumWindowsProc(HWND hwnd,LPARAM lParam)
{
    // call every child window (to find edit boxes)
    EnumChildWindows(hwnd,EnumWindowsProc2,lParam); 
    return TRUE;
}          

BOOL CALLBACK EnumWindowsProc2(HWND hwnd,LPARAM)
{
    ::SendMessage(hwnd,EM_SETPASSWORDCHAR,0,0); // reveal the password
    InvalidateRect(hwnd,NULL,FALSE);
    return TRUE;
}