Firstly right click on the file in question and choose "Data Entry Screen"
The data entry screen will open in "Rich Text" Mode:-
By clicking on "use raw" the editor will switch to raw HTML mode:-
Support for XPath as a standard field type has been added. When a field is marked as XPath then the XPath syntax highlighter will be used by default and the field value will be validated to be a valid XPath expression.
XPath syntax editor