[2023-02-24] Vertical markers in roadmaps (#34830)

Co-authored-by: Felicity Chapman <felicitymay@github.com>

content/issues/planning-and-tracking-with-projects/customizing-views-in-your-project/customizing-the-roadmap-layout.md

@@ -32,6 +32,21 @@ You can set the date or iteration fields that your roadmap will use to position
 1. Select a date or iteration field for "Start date" and "Target date."
 
   ![Screenshot showing the date field options](/assets/images/help/projects-v2/roadmap-select-dates.png)
+  
+
+{% ifversion projects-v2-roadmap-markers %}
+
+## Setting vertical markers
+
+You can configure vertical markers on a roadmap to show your iterations, the dates of items in your project, and the milestones associated with items in your project.
+
+1. In the top right of your roadmap, click {% octicon "location" aria-label="" %} **Markers**.
+  
+  ![Screenshot showing the menu bar in a roadmap layout. The "Markers" button is highlighted with an orange outline.](/assets/images/help/projects-v2/markers.png)
+  
+1. In the menu, select which markers you want to display on your roadmap.
+
+{% endif %}
 
 ## Setting the zoom level
 
@@ -55,12 +70,16 @@ You can sort items by a field value.
 
 {% endif %}
 
+{% ifversion projects-v2-roadmap-markers %}{% else %}
+
 ## Showing and hiding fields
 
 When you show and hide fields on the roadmap layout, you define which fields are shown when the side panel opens. This setting will not affect the information visible on the roadmap layout.
 
 {% data reusables.projects.customize.show-hide-field %}
 
+{% endif %}
+
 ## Grouping by field values
 
 You can group items by a custom field value.

data/features/projects-v2-roadmap-markers.yml

@@ -0,0 +1,5 @@
+# Issue 9539
+# Vertical markers on roadmaps, ability to move between iterations
+versions:
+  fpt: '*'
+  ghec: '*'

data/reusables/projects/about-roadmap-layout.md

@@ -1 +1,3 @@
-The roadmap layout provides a high-level visualization of your project across a configurable timespan, and allows you to drag items to affect their start and target dates. Roadmaps use your custom date fields to position your issues, pull requests, and draft issues on a timeline, allowing you to track work over time and watch progress.
+The roadmap layout provides a high-level visualization of your project across a configurable timespan, and allows you to drag items to affect their start and target dates{% ifversion projects-v2-roadmap-markers %} or selected iteration{% endif %}. Roadmaps use your custom date and iteration fields to position your issues, pull requests, and draft issues on a timeline, allowing you to track work over time and watch progress.
+
+{% ifversion projects-v2-roadmap-markers %}You can also display vertical lines to highlight key dates for your project, including iterations, milestones, and the dates of items in your project. These markers help you get a clear overview of your upcoming workload and how it's distributed across iterations or milestones.{% endif %}