Hi all,
I was just asked what kind of affiliation one needs to participate in the TEI conference. The answer is none at all. This is a digitization conference at which TEI members also meet rather than a meeting with lectures. We also very much encourage non-TEI-centric views: we regularly invite keynote speakers and accept papers that are critical of, sceptical of, or otherwise questioning about TEI activities or guidelines--or document modelling more generally. The range runs from highly technical to quite theoretical, so there should be scope for most active Digital Humanists.
So like many academic conferences, there is no need to be a member in order to participate. Of course you will have a chance to join the TEI at the conference if you wish! We might even let you drink the Koolaid ;)
-dan