Allows you access to the transform as a string.
The format of the string must be "m11 m12 m21 m22 mX mY".
To transform a point (x, y) to another point (x', y'), the
following formula is used:
x' = (x * m11) + (y * m21) + mX
y' = (x * m12) + (y * m22) + mY