Télécom ParisTech, France MediaWiki [1] is one of the leading open source wiki engines. It is well known for being used by Wikipedia but it also powers many other websites including Wikisource [2], the Wikipedia sister project dedicated to transcription, and the TEI wiki [3]. MediaWiki default encoding for wiki pages content is a flavor of wikitext. However the platform provides a powerful content abstraction system, allowing, e.g. to use an other content encoding for some or all wiki pages. The aim of this demo is to present a new MediaWiki extension, called "TEI" [4] that allows to create MediaWiki pages encoded in TEI P5 instead of Wikitext. This extension is a work in progress. It provides an implementation of a subset of TEI content tags (i.e. excluding the TEI header) inspired by TEI simplePrint. A simple XML editor is provided with validation and auto-complete based on a configurable ODD bundled with the extension. A beginning of WYSIWYG editor is also available. A demo wiki is updated daily with the latest version of the extension [5] and provides some examples. Before the demonstration we plan to improve both the WYSIWYG and XML editor, implement the support of more TEI tags and attributes and improve the extension configuration and extensibility. If time permits, we also plan to integrate it with ProofreadPage, an other MediaWiki extension providing a transcription workflow for MediaWiki and currently based on Wikitext [6]. [1] http://mediawiki.org/ [2] https://wikisource.org/ [3] https://wiki.tei-c.org/ [4] https://www.mediawiki.org/wiki/Extension:TEI [5] https://tools.wmflabs.org/wikitei/ [6] https://www.mediawiki.org/wiki/Extension:Proofread_Page