OptionalFieldFields it stands in for; it draws inside the section holding them.
OptionalInThe section it is placed in, replacing nothing.
OptionalReplacesTrue when it stands in for a section, tab or grid, so it draws in that place, not at a position.
OptionalSectionBlocks it stands in for; it draws in the place of the first.
OptionalSectionWhere inside its section it draws, for a placement in a section or a field claim.
OptionalSortOrder among panels in the same position, higher first. Absent means 0.
A panel already registered on this entity.