coreText

https://developer.apple.com/library/mac/documentation/TextFonts/Conceptual/CocoaTextArchitecture/FontHandling/FontHandling.html#//apple_ref/doc/uid/TP40009459-CH5-SW18

Querying Font Metrics

NSFont defines a number of methods for accessing a font’s metrics information, when that information is available. Methods such as boundingRectForGlyph:, boundingRectForFont, xHeight, and so on, all correspond to standard font metrics information. Figure 6-1 shows how the font metrics apply to glyph dimensions, and Table 6-1 lists the method names that correlate with the metrics. See the various method descriptions for more specific information