The "enabled" option -- referenced in yum(8), and used in default /etc/yum.repos.d/*.repo files -- is not documented in yum.conf(5). Presumably it should be listed under the "[server] options" section, with a description along the lines of: [[[ enabled either '1' or '0'. This tells yum whether or not it should try to use this repository. ]]]
Fixed in yum 2.1.12 - due out soon