xref

Sets the shape's x coordinate axis. If set to an x axis id (e.g. "x" or "x2"), the x position refers to an x coordinate. If set to "paper", the x position refers to the distance from the left side of the plotting area in normalized coordinates where "0" ("1") corresponds to the left (right) side. If the axis type is "log", then you must take the log of your desired range. If the axis type is "date", then you must convert the date to unix time in milliseconds.