t = cscaledfont:TextExtents(s$)
XAdvance and YAdvance values indicate the amount by which the
current point would be advanced by ccontext:ShowText().
Note that whitespace characters do not directly contribute to the
size of the rectangle as contained in the Width and Height fields
of the extents. They do
contribute indirectly by changing the position of non-whitespace
characters. In particular, trailing whitespace characters are
likely to not affect the size of the rectangle, though they will
affect the XAdvance and YAdvance values.
This function returns a table containing the text extents. See ccontext:TextExtents() for a description of all table members.