If the preceding value is non-zero, this value must be set in the range 256 - 32767 (inclusive). The third value enables applications to use a single name for the subfamily identified by the second value. If this value is zero, the remaining fields in the array will be ignored. All fonts which share a Preferred or Font Family name and which differ only by size range shall have the same subfamily value, and no fonts which differ in weight or style shall have the same subfamily value. The second value has no independent meaning, but serves as an identifier that associates fonts in a subfamily.
When there is a design size but no recommended size range, the rest of the array will consist of zeros. The first value represents the design size in 720/inch units (decipoints). In this usage, a family is a set of fonts which share a Preferred Family name (name ID 16), or Font Family name (name ID 1) if the Preferred Family name is absent. The size feature must be implemented in all fonts in any family which uses the feature. Required implementation: The Feature table of this GPOS feature contains no lookups its Feature Parameters field records an offset from the beginning of the Feature table to an array of five 16-bit unsigned integer values. Note that sizes refer to nominal final output size, and are independent of viewing magnification or resolution. Additional values serve to identify the set of fonts which share related size ranges, and to identify their shared name. The size range is useful in families which have fonts covering several ranges.
The design size is useful for determining proper tracking behavior. Function: This feature stores two kinds of information about the optical size of the font: design size (the point size for which the font is optimized) and size range (the range of point sizes which the font can serve well), as well as other information which helps applications use the size range.
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