As of version 4.0, in 2011,[16] Confluence ended support for wiki markup language.[17] This led to a sometimes-heated discussion by some previous versions' users who objected to the change.[18] In response, Atlassian provided a source code editor as a plugin, which allows advanced users the ability to edit the underlying XHTML-based document source.[19] However, although the new source markup is XHTML-based, it is not XHTML compliant.[20]