diff -up yum-3.4.3/docs/yum.conf.5.orig yum-3.4.3/docs/yum.conf.5

--- yum-3.4.3/docs/yum.conf.5.orig	2017-11-01 14:58:28.259740017 +0100

+++ yum-3.4.3/docs/yum.conf.5	2017-11-01 14:58:48.528648100 +0100

@@ -1356,8 +1356,17 @@ the same name. If the shell environment

 configuration file variable will not be replaced.

 .LP

-As of 3.2.28, any file in /etc/yum/vars is turned into a variable named after

-the filename (or overrides any of the above variables).

+When variable names are parsed in a string, all alphanumeric characters and

+underscores immediately following a $ sign are interpreted as part of a name.

+If a variable is undefined, it will not be replaced.

+For example, the strings $releasever-foo or $releasever/foo will be expanded

+with the $releasever value accordingly, whereas $releaseverfoo or

+$releasever_foo will not be expanded.

+

+As of 3.2.28, any properly named file in /etc/yum/vars is turned into

+a variable named after the filename (or overrides any of the above variables).

+Filenames may contain only alphanumeric characters and underscores

+and be in lowercase.

 Note that no warnings/errors are given if the files are unreadable, so creating

 files that only root can read may be confusing for users.