No seen any docs on it but I did a few tests a while ago and it picks up, subject, from, and text in the body and alt text.
But not any
aria- attributes, I though
aria-label might show up but it didn't.
There are a number of browser plugins available that block pixel tracking, often these are bundled as part of a larger Ad Block plugin. That could be what's causing the issue on the webmail clients.
I believe you can add a
<v:fill> not done much testing on it, just saw someone share it and made a note.
There's nothing wrong with
<script> tags it's more the contents of them that can be an issue, but some ESP's do insist on removing them everytime.
With the new Gmail annotations you have a choice of JSON or Microdata, Freshinbox has a similar tool to Litmus that outputs Microdata so you could use that instead.
One other possible thing, do you have images turned off?
If so when images are loaded there is a bug that the CSS no longer matches the HTML so no styles will work.
Strange, that's working fine for me, I quickly swapped the background colour to make it easier to see and the gmail one is definitely showing on Gmail.
As a side note, if you wanted to get the same layout in Gmail try adding
max-height: 0;margin-top:15px; to the same div that has the
class="gmail" and it'll flow over the next section.