Unfortunately, we cannot simply extend our editor like this because it is slightly different from the one used in Sitefinity. However, we are working on this missing feature and will provide it as soon as possible - expect it shortly after our Q1 release.
In the meantime, I suggest you the following:
Copy code directly from Visual Studio (preserving styles) or other code editing tool and paste in the content field in Lightning.
I hope this information helps.
the Telerik team
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