c99df3c4_nce_Guide___Configuring_Apache__Description
[Directive] JkEnvVar [Description] 
Adds a name and an optional default value of environment variable that should be sent to servlet-engine as a request attribute. If the default value is not given explicitely, the variable will only be send, if it is set during runtime. This directive can be used multiple times per virtual server. The default is empty, so no additional variables will be sent. Empty default values are supported since version 1.2.20. Not sending variables with empty defaults and empty runtime value has been introduced in version 1.2.21.
The Apache Tomcat Connector - Reference Guide - Configuring Apache
Description