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_CheckboxList :: __toString()
Overloads --to-string to return a CSV representation of the checked values. This implementation allows the field object to be echoed directly (MEOW_Field will forward to this method). This method is not intended to be called directly.