Merge pull request #13695 from MicrosoftDocs/ghogen-patch-592498

Add explanatory text for error condition and link to more information

Author: prmerger-automator[bot]

docs/msbuild/errors/msb4099.md

@@ -1,7 +1,7 @@
 ---
 title: "MSB4099 diagnostic code"
 description: "A reference to an item list at position 'value' is not allowed in this condition 'value'."
-ms.date: 12/06/2024
+ms.date: 3/11/2025
 ms.topic: "error-reference"
 f1_keywords:
  - MSB4099
@@ -26,14 +26,15 @@ This article describes the MSB4099 error code.
 
 ## Message text
 
-```output
-MSB4099: A reference to an item list at position 'value' is not allowed in this condition 'value'.
-```
+`MSB4099: A reference to an item list at position 'value' is not allowed in this condition 'value'.`
 
 <!-- :::editable-content name="postOutputDescription"::: -->
 <!--
 {StrBegin="MSB4099: "}
 -->
+This error occurs when a project is using an item in a condition in a context where it's not yet available for use. MSBuild evaluates a project file using multiple passes. `Import` elements, top-level `PropertyGroup` elements, and their `Property` elements are evaluated before items are evaluated. As a result, items are unavailable at the point when those elements are evaluated. Therefore, you can't use items in conditions in any of those elements. See [How MSBuild builds projects](../build-process-overview.md#evaluation-phase).
+
+To fix this issue, restructure your logic to avoid the need to reference an item in a condition in an `Import` element, `PropertyGroup` element, or `Property` element at the top level. 
 <!-- :::editable-content-end::: -->
 <!-- :::ErrorDefinitionDescription-end::: -->