Feature: #110816 - Highlight workspace changes in the frontend preview 

See forge#110816

Description 

The workspace preview notification in the frontend now contains a "Highlight changes" checkbox, showing the number of records on the page that have a version in the current workspace.

When switched on, changed records are outlined: new records with a solid, modified records with a dashed and moved records with a dotted line. For modified and moved records, the live version of the page is fetched once and the text of each changed record is compared with its live counterpart. Inserted words are highlighted, removed words are shown struck through at their former position. Switching the checkbox off restores the page as it was rendered. The choice is remembered in the browser.

Records rendered with the <f:render.record> or <f:render.contentArea> ViewHelpers and with the CONTENT or RECORDS content objects, for example styles.content.get , are covered. They are marked by event listeners to \TYPO3\CMS\Fluid\Event\ModifyRenderedRecordEvent and \TYPO3\CMS\Frontend\ContentObject\Event\AfterRecordIsRenderedEvent .

Deleted records are not rendered in the workspace preview and are therefore not highlighted.

Impact 

Changes of a workspace can be spotted directly in the frontend preview.

The records rendered in a workspace preview are wrapped in HTML comments, unless the preview notification is disabled with config.disablePreviewNotification = 1 . Frontend requests with ADMCMD_prev=LIVE by a logged-in backend user, which are used for the comparison, mark all rendered records. The comments are removed from responses which are not HTML pages.

Previews shared with a preview link without backend login only outline the changed records, the text is not compared.