Creates a mark at position where. If mark_name is null, the mark is anonymous; otherwise, the mark can be retrieved by name using k.TextBuffer.GetMark(string). If a mark has left gravity, and text is inserted at the current location of the mark, the mark will be moved to the left of the newly-inserted text. If the mark has right gravity (ie. left_gravity = false), the mark will end up on the right of newly-inserted text. The standard left-to-right cursor is a mark with right gravity (when you type, the cursor stays on the right side of the text you are typing).

Fires the TextBuffer.MarkSet event as notification of the initial placement of the mark.