In a Sitecore 8.2 (rev. 170614) instance an item was throwing the following error when selected in content editor:
Server Error in '/' Application. Data at the root level is invalid. Line 1, position 1. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Xml.XmlException: Data at the root level is invalid. Line 1, position 1.
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
The field that is associated with this item was filled in with plain text:
/sitecore/templates/System/Templates/Sections/Appearance/Appearance/__Preview. Removing the text in the dbbrowser made that error go away. It looks like the only way to add plain text to this field is through the dbbrowser from what I can see. Trying to edit the field from the content editor throws the above error message and stops the item from being saved if it is not recognized as xml. Is there any way to populate this field from Experience Editor/Content Editor with plain text that will not pass the xml validation in place?
I'm not sure if it matters but the item that had this applied to it was a datasource item being pointed to by a rendering on a page item.