src/vs/workbench/common/editor/sideBySideEditorInput.ts/SideBySideEditorInput/capabilities
class SideBySideEditorInput:	override get capabilities(): EditorInputCapabilities {

		// Use primary capabilities as main capabilities...
		let capabilities = this.primary.capabilities;

		// ...with the exception of `CanSplitInGroup` which
		// is only relevant to single editors.
		capabilities &= ~EditorInputCapabilities.CanSplitInGroup;

		// Trust: should be considered for both sides
		if (this.secondary.hasCapability(EditorInputCapabilities.RequiresTrust)) {
			capabilities |= EditorInputCapabilities.RequiresTrust;
		}

		// Singleton: should be considered for both sides
		if (this.secondary.hasCapability(EditorInputCapabilities.Singleton)) {
			capabilities |= EditorInputCapabilities.Singleton;
		}

		// Indicate we show more than one editor
		capabilities |= EditorInputCapabilities.MultipleEditors;

		return capabilities;
	}