xanchor

Sets the text box's horizontal position anchor This anchor binds the x position to the "left", "center" or "right" of the annotation. For example, if x is set to 1, xref to "paper" and xanchor to "right" then the right-most portion of the annotation lines up with the right-most edge of the plotting area. If "auto", the anchor is equivalent to "center" for data-referenced annotations or if there is an arrow, whereas for paper-referenced with no arrow, the anchor picked corresponds to the closest side. Default: auto.