188.8.131.52 X-UA-Compatible Processing Instruction
This functionality will not be implemented in any version of Microsoft Edge.
Windows Internet Explorer 10 and Internet Explorer 11 use
x-ua-compatible processing instruction to
switch the document mode of XML and XHTML documents:
This processing instruction (PI), in combination with other IE document mode settings, produces the following behavior for XML:
The x-ua-compatible PI can affect document mode just like the meta tag in HTML:
The X-UA-Compatible HTTP header can affect the document mode just like in HTML.
The minimum selectable document mode for XML is 9 (this differs from HTML).
Note that if the Browser Mode (set via CV List, CV Button, Dev Tools, Intranet, etc.) is less than IE9, then the legacy MSXML Mime Viewer will be used for "text/xml" documents regardless of any other versioning information.
Quirks emulation mode (QME) is not supported in XML documents.
The x-ua-compatible PI can only be preceded by the XML Declaration and/or whitespace, anything else causes it to be ignored.
The value of the x-ua-compatible PI must in the form of well-formed XML attributes, else it will be ignored.
Only the "content" attribute from the x-ua-compatible PI will be read, but other attributes are allowed.
The supported format for the "content" attribute on the x-ua-compatible PI must match the meta tag from HTML.
Using the x-ua-compatible PI prior to an XSLT transform sets the "ceiling" mode of the output from XSLT. For example if the PI opts into IE9 mode in Internet Explorer 10 and the transform produces HTML output with the HTML5 DOCTYPE, then that output will render in IE9 mode. Conversely if the output does not contain a DOCTYPE, it will render in Quirks Mode.