The HTML5 Canvas Text API - HTML5 Canvas - page 164

Remember, center is only the default alignment for the text. Because you can change this
with Text Arranger, the text can still be aligned in different ways while you are using the ap-
plication.
Figure 3-6 shows how a font set to start alignment with a middle baseline might appear on
the canvas.
Figure 3-6. Font with start alignment and middle baseline