The Editor does not accept full page HTML as its content and there are two reasons for this:
1. The Editor's editable area is an iframe element with its own <head> and <body> elements, which have some specific and required content or attributes.
2. The Editor provides the ability to edit visible
HTML content. A page <head> section does not contain any visible content, so there is no use in inserting it inside the Editor.
If you need to store and use full page HTML markup, then I suggest you to send only the <body> content to the Editor (without the <body> tag itself) and then add it back to the full page on the server, e.g. before saving to the database.
All the best,
the Telerik team
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