Will my old files work with P5?

1. <TEI.2> is now <TEI> and <teiCorpus.2> is now <teiCorpus>
2. TEI elements are in the http://www.tei-c.org/P5/ namespace
3. many attribute values seem to have changed… Y|N is now true|false
4. … or disappeared
   • text-valued attributes have become child elements
   • lang has become xml:lang
   • id has become xml:id
   • all IDREF (target) values have become URLs
   • the pointing elements seem to have disappeared!
5. The TEI pizza model has been cast aside and my extension files no longer work!

Why should I bother to switch?