doc: added a warning for the "share_all_vars" option for ngx.location.capture*.

Author: agentzh

README.markdown

@@ -2881,7 +2881,7 @@ argument, which supports the options:
 * `copy_all_vars`
 	specify whether to copy over all the Nginx variable values of the current request to the subrequest in question. modifications of the nginx variables in the subrequest will not affect the current (parent) request. This option was first introduced in the `v0.3.1rc31` release.
 * `share_all_vars`
-	specify whether to share all the Nginx variables of the subrequest with the current (parent) request. modifications of the Nginx variables in the subrequest will affect the current (parent) request.
+	specify whether to share all the Nginx variables of the subrequest with the current (parent) request. modifications of the Nginx variables in the subrequest will affect the current (parent) request. Enabling this option may lead to hard-to-debug issues due to bad side-effects and is considered bad and harmful. Only enable this option when you completely know what you are doing.
 * `always_forward_body`
 	when set to true, the current (parent) request's request body will always be forwarded to the subrequest being created if the `body` option is not specified. The request body read by either [ngx.req.read_body()](#ngxreqread_body) or [lua_need_request_body on](#lua_need_request_body) will be directly forwarded to the subrequest without copying the whole request body data when creating the subrequest (no matter the request body data is buffered in memory buffers or temporary files). By default, this option is `false` and when the `body` option is not specified, the request body of the current (parent) request is only forwarded when the subrequest takes the `PUT` or `POST` request method.
 

doc/HttpLuaModule.wiki

@@ -2320,7 +2320,7 @@ argument, which supports the options:
 * <code>copy_all_vars</code>
 : specify whether to copy over all the Nginx variable values of the current request to the subrequest in question. modifications of the nginx variables in the subrequest will not affect the current (parent) request. This option was first introduced in the <code>v0.3.1rc31</code> release.
 * <code>share_all_vars</code>
-: specify whether to share all the Nginx variables of the subrequest with the current (parent) request. modifications of the Nginx variables in the subrequest will affect the current (parent) request.
+: specify whether to share all the Nginx variables of the subrequest with the current (parent) request. modifications of the Nginx variables in the subrequest will affect the current (parent) request. Enabling this option may lead to hard-to-debug issues due to bad side-effects and is considered bad and harmful. Only enable this option when you completely know what you are doing.
 * <code>always_forward_body</code>
 : when set to true, the current (parent) request's request body will always be forwarded to the subrequest being created if the <code>body</code> option is not specified. The request body read by either [[#ngx.req.read_body|ngx.req.read_body()]] or [[#lua_need_request_body|lua_need_request_body on]] will be directly forwarded to the subrequest without copying the whole request body data when creating the subrequest (no matter the request body data is buffered in memory buffers or temporary files). By default, this option is <code>false</code> and when the <code>body</code> option is not specified, the request body of the current (parent) request is only forwarded when the subrequest takes the <code>PUT</code> or <code>POST</code> request method.