Hi Alfonso,

The Kendo UI for Angular Editor allows the developer to create custom tools. However, based on the operation that this tool should execute, there are certain limitations and specifics that come from the ProseMirror library (which the Editor used under the hood). 

Internally, we set the Editor to support many HTML tags such as <p>, <ul>, <li>, etc. which is done thorugh the ProseMirror schema. Registering new HTML tags is possible by customizing this schema. Please check out the following article on how to customize the ProseMirror schema and allow the Editor to support different HTML tags (in this case <iframe>).

https://www.telerik.com/kendo-angular-ui/components/editor/schema/#toc-editor-schema

The ProseMirror is a third-party library which we didn't provide support for. I understand that this might be found disappointing to some extent but let me add a bit more details as to why. Since we use the features of the ProseMirror library to create the Kendo UI for the Angular Editor component, we exposed properties for customizing the underlying schema. Thus the developer can gain full control over the library as well as the Editor component itself. However, the ProseMirror has its own API properties and support. That is why any further ProseMirror schema modifications have limited support.

Due to the specific nature of the request and the fact that the developer can modify the supported tags, I am declining the feature request.

Regards,
Martin
Progress Telerik