Quite often we receive requests from our clients asking how to disable the proofreading option in the source mode of a rich text editor and keep it enabled only in the WYSIWYG mode. In general, for such cases, we offer a special option disableAutoSearchIn of WProofreader that allows disabling it for certain cases (class, id, data attribute name and HTML elements).
Disabling WProofreader in Source Mode of CKEditor 4
The source mode of CKEditor 4 has a special CSS class '.cke_source'. You can rely on this class and disable WProofreader using the disableAutoSearchIn option with this class specified as in the example below.