The mode can be static, progressive, or wrap.
Static. The image generated will not be constrained. The dimensions will be large enough to fit all text passed. This is the default mode.
Progressive. The text size used for the generated image will be reduced until it will fit within the HTML elements bounds. The text size will not be increased if it doesn't fill the elements bounds.
Wrap. If the text is wider than the HTML elements bounds at the passed font size it will be wrapped at the appropriate spots. Wrap can also take advantage of center and right aligned text.