IE10 Enterprise Mode document mode selection for legacy intranet applications

IE10 Enterprise Mode Configuration Boundary

IE10 introduced Enterprise Mode as a mechanism to force specific document modes (IE7, IE8, IE9, or IE10) for legacy web applications that require older rendering engines. This feature operates alongside Compatibility View settings and the X-UA-Compatible meta tag, creating a hierarchy of mode selection that can produce ambiguous results when multiple triggers are present.

The documented behavior shows that Enterprise Mode can be activated through Group Policy, the Enterprise Mode Site List Manager, or programmatically via the X-UA-Compatible header. However, the specification does not clearly define the precedence order when a site is simultaneously listed in an Enterprise Mode site list and contains an X-UA-Compatible meta tag declaring a different mode.

Additionally, frame-based applications present a complication where nested frames may inherit or override document modes independently of the parent page's declared mode, potentially causing inconsistent rendering within a single page. The interaction between these mechanisms—particularly when GPO settings, site lists, and meta tags conflict—remains an unresolved decision point for administrators managing legacy applications.

Which mechanism takes precedence when Enterprise Mode is configured through both a site list and an X-UA-Compatible meta tag, and how does frame inheritance affect the final rendered document mode?