This paper chronicles the work of the TEI textual criticism working groups through several phases, documenting how and why the design goals were shaped by the requirements of several distinct user communities and by the nature of the textual evidence itself. Encoding schemes for the representation of physical details of textual witnesses were unified with encoding schemes for critical editing practices when it was observed that the two phenomena were inextricably layered and linked within real texts. Rationale is offered for the development teams' adherence to exceedingly general design principles: (a) the requirement that the encoding notations be neutral in text-theoretic terms; (b) the need to accommodate dramatically different text-transmission phenomena and research goals within diverse text-critical arenas; (c) the need for commensurability of the text-critical markup with encoding notations used in closely related text-analytic research. The paper also assesses the results of the effort in terms of the encoding scheme's adequacy for several scholarly purposes: suggestions are made concerning the need for programmatic testing, for refinement, and for extension of the encoding model to support a broader range of text-transmission phenomena and research objectives.