aspnet_client:
http://lixiao2011.blog.163.com/blog/static/178193044201211133553121/
http://blog.csdn.net/jrl5365/article/details/1526884
http://msdn.microsoft.com/en-US/library/k6h9cz8h%28v=VS.80%29.aspx
http://msdn.microsoft.com/en-us/library/aa478975.aspx
http://msdn.microsoft.com/en-us/library/aa719700%28v=VS.71%29.aspx
http://msdn.microsoft.com/en-us/library/k6h9cz8h%28v=vs.71%29.aspx
To understand the utility of these two methods, consider the ASP.NET validation Web controls RequiredFieldValidator, RegularExpressionValidator, and so on. These controls rely on a common validation JavaScript file, WebValidation.js, which is found in the aspnet_client/system_web/version_number directory of an ASP.NET Web application.
If you have multiple versions of the SDK installed, you will see multiple subdirectories under aspnet_client/system_web. Because a control library is tied to a specific version of the script file, the recommended deployment pattern allows different versions of a control library to run side by side.
Note also that one aspnet_client directory is created for each Web site hosted on the computer. Generally a server hosts only one Web site. However, more than one site is permissible, and multiple sites lead to multiple copies of the aspnet_client directory.
Client-side script, such as client-side validation, can be installed and removed using Aspnet_regiis.exe. To install the client-side script for the version of ASP.NET associated with the tool to the aspnet_client subdirectory of each IIS site directory, use the -c option. To remove the client-side script for just the ASP.NET version associated with the tool, use the -e option. To remove the client-side script for all installed versions of ASP.NET, use the -ea option.
来源：https://www.cnblogs.com/daishuguang/archive/2013/04/12/3016222.html