Hi Markus Berchtold,
There are a couple of ways to achieve, what you need.
Sitefinity makes it quite easy to upload and reuse User controls or Custom
controls within your projects.
What you need to do is to create and upload your user
controls as described in the article below:
It is entirely up to you if you would like to upload a user
control (.ascx) or Custom control (compiled .dll).
Moreover you also have the ability to upload your Master
pages and use them as a template for your pages, in almost the same way as you
would have done for your non Sitefinity projects.
For more information:
Another option is extending the built-in controls in
Sitefinity and providing additional functionality to meet your requirements.
For more details, please have a look at:
Hope that helps!
the Telerik team
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