Unable to un-strike or un-underline saved content.

To repeat:

• Create a document using CKEditor, add some text which is struck using the strikethrough feature
• Save and view the document
• Return to edit mode and attempt to un strike the text

The issue seems to be related to the rendering engine, where strike is being represented in HTML as <del> tag. CKEditor does not know what to do with this tag and ignores it. CKEditor instead uses <s>.

Same issue seems to be present with underlined text. CKEditor creates text with <u> tag and then XWiki rendering engine converts this to <ins> tag which is equally valid but not recognized by CKEditor as underlined text which should be able to be un-underlined.