.Net Web.config attributes case-sensitive

One little tidbit I learned this morning:
In the Web.config file for web applications the attribute values are case sensitive.
To aid remote debugging I turned "off" the friendly messages to get meaningful error messages from remote machines. I tried the following line, but it didn't work:

   <customErrors mode="off"/>

It turns out the attribute values are case-sensitive. The line should be:

   <customErrors mode="Off"/>