Clarify OutputCache intent and limitations for classic ASP.Net.

[StephenMolloy]

This pull request updates the XML documentation for several ASP.NET output caching-related types to clarify the intended use and limitations of the VaryBy settings. The main focus is to add prominent warnings that output caching and its variation mechanisms are meant for performance optimization and not for isolating personalized or sensitive content. Additional clarifications are also made to some remarks for better accuracy.

Documentation improvements and warnings

Security and usage warnings:

• Added a new [!IMPORTANT] note to the remarks of all affected types, explaining that output caching and VaryBy settings are for performance optimization only, and should not be relied upon to isolate personalized, tenant-specific, authorization-dependent, or sensitive responses. Explicit isolation must be enforced independently of cache configuration. [1] [2] [3] [4] [5] [6] [7] [8] [9]

Clarifications to remarks:

• Improved the explanations for how VaryByHeaders and VaryByParams work, specifying that they store and serve the appropriate representation of a resource for a given request, and clarifying the types of request data used for variation. [1] [2]
• Updated language in the OutputCache.xml remarks to use "alternate representations" instead of "different versions" for greater precision.

These changes help prevent misuse of output caching for security or isolation, and make the documentation clearer for developers.

[Copilot]

Pull request overview

This pull request updates the classic ASP.NET (System.Web) API reference XML to clarify the intent and limitations of output caching variation (VaryBy*), emphasizing that it’s a performance optimization mechanism and must not be treated as a security/isolation boundary.

Changes:

• Added prominent [!IMPORTANT] warnings across output-caching-related types about not using VaryBy to isolate personalized/tenant-sensitive/authorization-dependent responses.
• Refined remarks for VaryByParams and VaryByHeaders to better describe what request data participates in cache variation and how alternate representations are served.
• Improved wording in System.Web.Caching.OutputCache remarks (e.g., “alternate representations”).

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
xml/System.Web/HttpCacheVaryByParams.xml	Clarifies VaryByParams behavior and adds an IMPORTANT warning about non-security usage.
xml/System.Web/HttpCacheVaryByHeaders.xml	Clarifies VaryByHeaders behavior and adds an IMPORTANT warning about non-security usage.
xml/System.Web/HttpCacheVaryByContentEncodings.xml	Adds an IMPORTANT warning about non-security usage of cache variation.
xml/System.Web/HttpCachePolicy.xml	Adds an IMPORTANT warning in SetVaryByCustom remarks about non-security usage of cache variation.
xml/System.Web.UI/PartialCachingAttribute.xml	Adds an IMPORTANT warning about non-security usage of cache variation.
xml/System.Web.UI/OutputCacheParameters.xml	Adds an IMPORTANT warning about non-security usage of cache variation.
xml/System.Web.Configuration/OutputCacheSection.xml	Adds an IMPORTANT warning about non-security usage of cache variation.
xml/System.Web.Configuration/OutputCacheProfile.xml	Adds an IMPORTANT warning about non-security usage of cache variation.
xml/System.Web.Caching/OutputCache.xml	Refines remarks wording and adds an IMPORTANT warning about non-security usage of cache variation.

[gewarren]

@StephenMolloy The merge conflicts might be because we split the .NET Framework APIs into a separate repo - dotnet/dotnetfw-api-docs.