purposes additions to TPE

As requested in the last call I have created a PR against master for the
purpose changes.

This is a readable snapshot of the document showing the TPE if the PR is
merged:

https://w3c.github.io/dnt/drafts/purposes-snapshotmay2018.html

See 5.2.1, 5.2.2, 6.6.1 and 7.5.10

Mike

Received on Monday, 7 May 2018 10:36:12 UTC