Even if you’ve chosen the TEI for your project, there are further choices to make about exactly how you use it. Selecting the components you need remains important: your documents should not use every defined element. The existence of the <date> element does not imply the obligation or recommendation that every date in a text be tagged as such; some TEI elements are required in certain contexts, but a great many are optional, and it is intended that their use be left to the scholar’s judgment. Extra markup is costly, so project must decide just which features need to be marked in order to serve its scholarly ends. It is tempting to add markup that has no specific application but that might be of interest to someone in the future; but only the especially well-funded project can afford this luxury. Apart from the expense, it is worth considering how useful the encoded information will be to other scholars. Seeing the feature in question differently, they might want to develop their own encoding. Personal names, for example, may seem at first a straightforward category that requires little extra time to tag; but scholars who have worked on encoding personal names have found them to be hard to define and delimit (Lavagnino 2006, 335).
One of the important goals in revising the existing Guidelines and developing P5 had been the simplification of the customization process which was difficult to understand and tedious to implement in previous versions. The TEI Council accordingly spent considerable time in designing and implementing the new class-based modular infrastructure building blocks. In this new system, customization is not an afterthought but is required for virtually every use of the TEI (Wittern et al. 2009, 293).