Masterpress 1.3.6 is a compatibility release. It resolves an edge case with shared fieldsets not working for MySQL 8 when the fieldset is limited to more than 1 post type or taxonomy or excluding any post types or taxonomies.
MPFT_RelatedSite :: offsetExists( Integer $index )
Checks if the numerical array offset exists for the sites selected in the UI. Since this overrides offset-exists the offset test can be made by calling isset directly on the field object.
Note: This method is intended for internal use and should not be called directly.