Whether the mark has left gravity. When text is inserted at the mark’s
current location, if the mark has left gravity it will be moved
to the left of the newly-inserted text, otherwise to the right.
Optional name
name?:string
The name of the mark or %NULL if the mark is anonymous.
Whether the mark has left gravity. When text is inserted at the mark’s current location, if the mark has left gravity it will be moved to the left of the newly-inserted text, otherwise to the right.