由于写了输入法的blog，很多人问这个问题：如何某个窗口发送字符？
在MSDN上搜索VK_PACKET可得：
VK_PACKET E7
Used to pass Unicode characters as if they were keystrokes. If VK_PACKET is used with SendInput, then the Unicode character to be delivered should be placed into the lower 16 bits of the scan code. If a keyboard message is removed from the message queue and the virtual key is VK_PACKET, then the Unicode character will be the upper 16 bits of the lparam.
