TEI Roma is a tool for working with TEI customizations. A TEI customization is a document from which you can generate a schema defining which elements and attributes from the TEI system you want to use, along with customized HTML or PDF documentation of it. The schema generated can be expressed in any of DTD, RELAXNG W3C Schema or Schematron languages.
A TEI customization is informally referred to as an ODD (for "One Document Does it all")