THE_REQUEST

[1] mod_rewrite - Apache HTTP Server Version 2.5 (2017-08-18 17:24:45 +09:00) <https://httpd.apache.org/docs/trunk/mod/mod_rewrite.html#RewriteCond>

THE_REQUEST
The full HTTP request line sent by the browser to the server (e.g., "GET /index.html HTTP/1.1"). This does not include any additional headers sent by the browser. This value has not been unescaped (decoded), unlike most other variables below.

[2] HTTP/0.9 や HTTP/2 の時どうなるのだろう。