This window shows how this Extended UI Module will appear at runtime with data for the selected asset. It's important that you use this tool to ensure the Extended UI Module displays as expected at runtime.
If the content source object - either a Custom object or Custom application - is not correctly configured to render asset data in the module for whatever reason, this preview window will indicate the issue.
For example, if you do not specify a valid file as the Index File Name for a custom application, then this window displays the errors that would appear in the Asset dashboard: HTTP Status 404 - Invalid entry (The requested resource (Invalid entry) is not available.) Again, its important that you double-check the content source settings for an Extended UI Module to make sure they're defined correctly.
The extended UI module shown in the preview window has a set width of 230 pixels. During runtime, the position of the Extended UI Module in the Asset dashboard determines its width: 210 pixels for left column modules and 230 pixels for right column modules. If you position the module in the center column, the width will be the total width (of the user's defined screen resolution) minus the width of the left and right columns. For example, if the user's screen has a width of 1920 pixels, then the center column modules will have a width of 1480 pixels.
When you are done viewing the module in the preview window, click Close. you return to the Extended UI Module wizard, preview page.