Last Updated: 06 Jul 2017 07:26 by ADMIN
Marin Bratanov
Created on: 07 Nov 2016 12:40
Category: UI for ASP.NET AJAX
Type: Feature Request
Lightweight RenderMode will not fall back to Classic when the X-UA-Compatible header with value IE=edge is present
At present, when IE is in Compatibility Mode the UI for ASP.NET AJAX controls use the Classic RenderMode in all cases because of the User Agent string the browser provides.

If RenderMode="Lightweight" and the X-UA-Compatible meta tag with value "IE=edge" is present on the server, the controls will render in the Lightweight mode instead of falling back to Classic.
This will also apply to RenderMode="Auto".
Marin Bratanov
Posted on: 06 Jul 2017 07:26
We ship fixes and improvements in the first official release after their implementation (, so, I am afraid, it will not be available as a patch.
Simon Vane
Posted on: 05 Jul 2017 15:54
Thanks Marin. 

Will this be available as a patch to 2017.1.118?

Marin Bratanov
Posted on: 05 Jul 2017 14:12
You are completely right, Simon, we will fix this for R2 2017 SP2
Simon Vane
Posted on: 05 Jul 2017 09:39
Please note, the code does a case sensitive compare of "IE=Edge" of the X-UA-Compatible header so the value must be "IE=Edge" not "IE=edge".

This conflicts with the Microsoft documentation -

This is a bug and the code should be doing a cases insensitive compare I think.

Also not that the header needs to be added early in the page lifecycle in WebForms before the controls are created e.g. PreInit.