本页面总结了求生之路二代附加组件的变化。
L4D2 的 add-on 中的 addoninfo.txt 文件必须包含正确的应用程序ID：
addonSteamAppID 550
如果没有这一行，或是设置成了求生之路一代的ID（500），当用户双击VPK文件时将无法安装到正确位置。
如果用户在游戏没有运行时双击打开 .VPK 文件，它将会被复制到一个临时的位置：
Steam\steamapps\SourceMods\addons
当求生之路一代或二代启动时，它们会在上述路径中搜索 add-on，并且复制到各自的正确路径下。
This summarizes the changes for 
求生之路2's Add-ons from 
求生之路's.
The addoninfo.txt file in your L4D2 add-on must have the proper app ID:
addonSteamAppID 550
If this isn't included, or if it's set to the Left 4 Dead 1 ID (500), VPK files will not be installed properly when users double click on them. (Or technically, theaddoninstaller.exeprogram.)
If users double click a VPK while the game is not running, it gets copied to a temporary location under:
Steam\steamapps\SourceMods\addons
Then, when 
are launched, they look for add-ons in those directories, then moves them over to their own respective add-ons folder.
