Why Does Setting FEATURE_BROWSER_EMULATION to IE10 or IE11 Cause Web Browser Control Malfunction?

Investigating the Web Browser Control Emulation Issue with FEATURE_BROWSER_EMULATION

Context

Web browser controls, when used within applications, often require specific compatibility settings to support the rendering of web content. FEATURE_BROWSER_EMULATION is a registry setting that allows developers to control the browser mode that the web browser control uses. However, certain values set for this feature can cause emulation issues.

The Problem

A user encountered a situation where setting FEATURE_BROWSER_EMULATION to IE10 or IE11 values caused a web browser control to malfunction. Specifically, a month date picker on the Dojo Toolkit calendar demo site ceased to function. The control worked correctly without any FEATURE_BROWSER_EMULATION setting or when set to IE9 emulation.

The Solution

The problem was resolved by disabling the FEATURE_NINPUT_LEGACY_MODE registry setting along with optimizations and enhancements for the WebBrowser control. Here's a detailed examination of the implemented changes:

1. Disable FEATURE_NINPUT_LEGACY_MODE: By default, this setting is enabled, but disabling it ensures support for the NINPUT API in the web browser control.
2. Enable CLIPCHILDREN and GPU_RENDERING: These settings enhance performance by allowing the browser control to use accelerated rendering and clipping. Developers must balance these features against potential compatibility issues.
3. Enable AJAX_CONNECTIONEVENTS and WEBOC_DOCUMENT_ZOOM: These settings enhance web application responsiveness and allow for dynamic resizing of web pages, respectively.

The following code sample demonstrates how to set these registry values in C#:

<code class="c#">const string FEATURE_BROWSER_EMULATION = @"HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\FeatureControl\";
        
Registry.SetValue(FEATURE_BROWSER_EMULATION + "FEATURE_BROWSER_EMULATION", appName, GetBrowserEmulationMode(), RegistryValueKind.DWord);
Registry.SetValue(FEATURE_BROWSER_EMULATION + "FEATURE_ENABLE_CLIPCHILDREN_OPTIMIZATION", appName, 1, RegistryValueKind.DWord);
Registry.SetValue(FEATURE_BROWSER_EMULATION + "FEATURE_AJAX_CONNECTIONEVENTS", appName, 1, RegistryValueKind.DWord);
Registry.SetValue(FEATURE_BROWSER_EMULATION + "FEATURE_GPU_RENDERING", appName, 1, RegistryValueKind.DWord);
Registry.SetValue(FEATURE_BROWSER_EMULATION + "FEATURE_WEBOC_DOCUMENT_ZOOM", appName, 1, RegistryValueKind.DWord);
Registry.SetValue(FEATURE_BROWSER_EMULATION + "FEATURE_NINPUT_LEGACYMODE", appName, 0, RegistryValueKind.DWord);</code>

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