To begin to understand how this works, here is a screenshot of a search for a U.S. Federal Census record:
As you can see the basic information from the record has been extracted in the index entry, seen above. You can also view the image of the original record. This is important because the extracted information may not be correctly interpreted from the document itself. Here is the view of the document accessed by clicking the link.
The new part of this experience is the added indexed area outlined in red. Now there is no need to switch back to the first indexed view of the record. You can see exactly what the indexer interpreted from the record. Now, all that is needed is a way to enter an alternate reading of the document if the information in the index is wrong. Since this is a record about my family, I am more likely able to accurately read the handwriting of the original document, so it would be very helpful to be able to attach a "alternate reading." It would be even more helpful if the alternate reading then became searchable.
This is a great step by FamilySearch. As stated by FamilySearch in the post:
Volunteers have indexed billions of names from historical records that have been digitized and made available at FamilySearch.org. The indexing process makes key pieces of information from the original record searchable using modern technology, so researchers can find a record based on name, date, location, relationships, and other key pieces of information. While these indexes are invaluable, those reviewing records must still compare the index with the digitized image to ensure the index is accurate and to discover additional information that was not indexed. Prior to this new improvement, the indexed information and the actual digital image were only found on separate web pages. This meant that comparing the two versions of information required navigating back and forth between the index and the image or opening up multiple tabs or browser sessions to compare the pages side by side.
Now, the new hybrid record view makes the information that was indexed from an historical record visible when reviewing the digitized image of the record. This is achieved by creating a split pane, where the index appears below the image.