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Sitefinity uses ASP.NET Master Pages and Themes to make templates. We recommend making templates the same way that the included master pages and themes were created. For more info on templates, please watch this webinar
For User Controls design considerations, we recommend making any variables public properties. This ensures that the end user can complete a form to use the control. Sitefinity offers property selectors, so users can select files and URLs if they'd like. For more info on these selectors, please read these posts
. To extend on this model, you can also create control designers. These forms are more user friendly. For more info, please read this post
and watch this webinar
the Telerik team