Some characters such as y and g have descenders that drop below the baseline. A TextLayout object has methods for returning information about the baseline of the text. The methods support writing systems that use different baselines, and multiple such writing systems in the same line of text. The baselines supported are Roman, centered, and hanging. Roman text uses the baseline that runs under the bottoms of the characters that do not have descenders.
Chinese text uses a centered baseline that runs through the centers of the characters.
The hanging baseline is used for languages, like Hindi, which generally align at the top. Currently, a TextLayout object uses the Roman baseline no matter what language the text is in. Many fonts assume the Roman baseline too, so these methods exist for typographic features that are not currently in widespread use. When TextLayout supports the Roman, centered, and hanging baselines, you will be able to use the information returned by these methods to align a line of text that uses different baselines. Ascent, Descent, and Leading Ascent, descent, and leading are properties of fonts.