Static kCTTrackingAttributeName 

pub unsafe static kCTTrackingAttributeName: &'static CFString

Available on crate feature CTStringAttributes only.

Applies tracking (letterspacing).

Value must be a CFNumber. Default is zero (no tracking). The tracking attribute indicates how much additional space, in points, should be added to each character cluster after layout. The effect of this attribute is similar to kCTKernAttributeName but differs in that the added tracking is treated as trailing whitespace and a non-zero amount disables non-essential ligatures unless overridden by kCTLigatureAttributeName being present. If both kCTKernAttributeName and kCTTrackingAttributeName are present kCTKernAttributeName will be ignored unless zero; kCTTrackingAttributeName will still be honored.

See also: kCTKernAttributeName

See also: kCTLigatureAttributeName

See also: CTLineGetTrailingWhitespaceWidth

See also Apple’s documentation