Different IE5-Quirks-Modes in IE 11?

Question

Situation: We have a legacy web application that does not set any doctype and therefore sends browsers to quirks mode, which we need to get working in IE 11. According to this article:

https://technet.microsoft.com/en-us/itpro/internet-explorer/ie11-deploy-guide/deprecated-document-modes

IE 11 should go to its IE5 quirks mode in this case. Additionally to leaving out any doctype, it is possible to explicitly send IE 11 to a quirks mode via e.g.:

<META content="IE=5" http-equiv="X-UA-Compatible">

...in this case setting the IE 5 quirks mode explicitly.

Observation: Layout and behaviour of our web application changes in IE 11 depending on whether or not we set the META tag as above. With the META-tag we get a different layout and performance problems.

Question: Shouldn't IE 11 behave exactly the same, namely according to its IE 5 quirks mode, if you don't set a doctype regardless of the presence of the META tag?

Any hint would be welcome :-)

Answer 1

Silly me, if one actually follow the flow chart on the page

https://technet.microsoft.com/en-us/itpro/internet-explorer/ie11-deploy-guide/deprecated-document-modes

one sees that IE 11 defaults to a "Interoperable (HTML5) quirks mode" instead of IE 5 quirks mode, see:

https://msdn.microsoft.com/en-us/library/hh869300(v=vs.85).aspx