At the top-left of the XML Editor, you can click to preview a topic based on the output format used in any of the targets in your project.
When you preview for a specific target, the condition tags set for that target are automatically used in the preview. However, if you want to test the output with certain condition tags included or excluded, click in the Preview dialog. The Conditional Text dialog opens. Either the Basic or Advanced mode is already selected, depending on which mode is being used in the target. You can use the same steps that are used in the target for including and excluding certain condition tags.
Changes in the Preview window pane are not transferred to the target settings. They're simply temporary so that you can see what a topic looks like with certain condition settings.