A character string identifying the
reference point for the text being drawn. The first character in
this string identifies the reference position in the "up" direction
and may be "B" (baseline), "C" (centre), "T" (top) or "M" (bottom).
The second character identifies the side-to-side reference position
and may be "L" (left), "C" (centre) or "R" (right ). The string is
case-insensitive, and only the first two characters are significant.
For example, a value of "BL" means that the left end of the
baseline of the original (un-rotated) text is to be drawn at the
position given by POS.