cups - Add support for CUPS (Common Unix Printing System)
debug - Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Backtraces
eds - Enable support for Evolution-Data-Server (EDS)
plugins - Enable plugins build (see http://www.abisource.com/wiki/PluginMatrix for more information). If your file cannot be opened due lack of support, try enabling this.
readline - Enable support for libreadline, a GNU line-editing library that almost everyone wants
redland - Enables support redland and raptor libs.