pelo que pesquisei rapidamente na doc. do apache
"Special Purpose Environment Variables
Interoperability problems have led to the introduction of mechanisms to modify the way Apache behaves when talking to particular clients. To make these mechanisms as flexible as possible, they are invoked by defining environment variables, typically with BrowserMatch, though SetEnv and PassEnv could also be used, for example."
downgrade-1.0
This forces the request to be treated as a HTTP/1.0 request even if it was in a later dialect.
force-response-1.0
This forces an HTTP/1.0 response to clients making an HTTP/1.0 request. It was originally implemented as a result of a problem with AOL's proxies. Some HTTP/1.0 clients may not behave correctly when given an HTTP/1.1 response, and this can be used to interoperate with them.
Se errei por favor me corrijam.
#vamobuscarfellas
O primeiro colega foi 100% acertivo em sua busca, abaixo segue documentação resumida sobre as variáveis dentro do servidor de aplicação,sugiro aos nobres colegas de estudo que deem uma olhada com calma nas demais variáveis, algumas delas como a de compressão podem ser objeto de questões.
Na literalidade, o que está no site do Apache: https://httpd.apache.org/docs/2.4/env.html
Environment Variables in Apache
There are two kinds of environment variables that affect the Apache HTTP Server.
First, there are the environment variables controlled by the underlying operating system. These are set before the server starts. They can be used in expansions in configuration files, and can optionally be passed to CGI scripts and SSI using the PassEnv directive.
Second, the Apache HTTP Server provides a mechanism for storing information in named variables that are also called environment variables. This information can be used to control various operations such as logging or access control. The variables are also used as a mechanism to communicate with external programs such as CGI scripts. This document discusses different ways to manipulate and use these variables.
Although these variables are referred to as environment variables, they are not the same as the environment variables controlled by the underlying operating system. Instead, these variables are stored and manipulated in an internal Apache structure. They only become actual operating system environment variables when they are provided to CGI scripts and Server Side Include scripts. If you wish to manipulate the operating system environment under which the server itself runs, you must use the standard environment manipulation mechanisms provided by your operating system shell.
Special Purpose Environment Variables
Interoperability problems have led to the introduction of mechanisms to modify the way Apache behaves when talking to particular clients. To make these mechanisms as flexible as possible, they are invoked by defining environment variables, typically with BrowserMatch, though SetEnv and PassEnv could also be used, for example.
downgrade-1.0
This forces the request to be treated as a HTTP/1.0 request even if it was in a later dialect.
force-response-1.0
This forces an HTTP/1.0 response to clients making an HTTP/1.0 request. It was originally implemented as a result of a problem with AOL's proxies. Some HTTP/1.0 clients may not behave correctly when given an HTTP/1.1 response, and this can be used to interoperate with them.