By default, images and text in fixed-layout EPUB are written into the page as 'live elements', meaning text has a font and style and can be selected and searched, and images have a position in the reading order and can have descriptions added.
This is typically the best approach for achieving accessible content, however this may not always be desirable. e.g. perhaps the text uses an unsupported font format or styling or images have been drawn in InDesign.
Moving InDesign objects onto a layer named FLO_BASE causes them to be flattened into one large background graphic. Any objects on the FLO_BASE layer are merged together and flattened into a single JPEG image at the export size of the page, set in the Preferences panel.
After exporting to text is not live or searchable and images do not have alt text applied.
Setting the Prefer InDesign live text option to no in the CircularFLO Preferences Panel has a similar affect across the whole document, means all text becomes embedded, not live.
The Make FLO_BASE layer tool and the Lift live text from base artwork tool in the CircularFLO Document Tools create and work with the FLO_BASE layer.