User Guide

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Here is a description of each value:
Typo Ascender
This is the typographically-correct ascender value. It is the
topmost line of lowercase characters, usually, the topmost line
of the ‘b’ character.
Typo Descender The same as Typo Ascender, but for the lowest line. Usually it
is equal to the bottom line of the character ‘p’.
Typo Line Gap
“Typographically” correct line gap value (distance between
bottom line of the upper line of text and top line of the lower
line of text).
WinAscent [OS/2] This value defines the topmost line of all important
characters in the font. “Important” characters are all non-
exceptional characters. For example, if most of the characters
have the topmost position at 900 font units and one, not often
used character, has it at 1300 font units, it’s a good idea to set
WinAscent at 900 units. Note that in most cases portions of
the characters that are above the WinAscent value will not
appear on the screen or print on some printers. Please note
that WinAscent is NOT a typography ascender, usually
measured as the topmost line of lowercase characters. It is
mostly a technical parameter used by the rasterizer to allocate
vertical space to render characters.
WinDescent [OS/2] The same as WinAscent, but for the lowest line of all
“normal” characters.
Ascender
[hhea] This value is used by the Mac OS in about the same
situation as Windows uses the WinAscent value from the
OS/2 table – to define the topmost position of all important
glyphs.
Descender [hhea] In short: the Macintosh version of the Windows
WinDescent parameter. If there are any pixels below this line
the glyph will be squashed in the vertical direction to match
metrics defined by the Ascender and Descender parameters.
Line Gap [hhea] This value is used by the Mac OS to compensate
Ascender and Descender values and calculate the correct
distance between baselines of the text. Refer to the formulas
below to see how baseline-to-baseline distance is calculated.