Fallback for OpenType MATH constants

Correspondance in TeX OpenType suggested default Firefox fallback WebKit fallback Chromium fallback MathPlayer MathML/CSS proposal
rule thickness ξ8 ?? height of U+00AF MACRON if in the interval (0, x-height) or 40/430.556 x-height otherwise. 0.05em Same as WebKit 5% font size ??
scriptPercentScaleDown Per-font macro 80% Unused Unused Unused scriptsizemultiplier from MathML (default 0.71) 0.8
scriptScriptPercentScaleDown Per-font macro 60% Unused Unused Unused scriptsizemultiplier from MathML (default 0.71) -- used twice 0.6
delimitedSubFormulaMinHeight σ21 normal line height × 1.5 Unused Unused Unused Unused Unused
displayOperatorMinHeight ?? None 0, additional heuristic 0, additional heuristic Unused Unused (chars are already larger) 0, with additional heuristic
mathLeading Unused None Unused Unused Unused ?? Unused
axisHeight σ22 (axis height) None ½ the height of U+2212 MINUS SIGN if in the interval (0, x-height) ; otherwise 250/430.556 the x-height. ½ x-height Same as WebKit middle of '=' ??
accentBaseHeight σ5 (x-height) x‑height of the font (os2.sxHeight) plus any possible overshots. x-height x-height Same as WebKit x-height x-height
flattenedAccentBaseHeight ?? (capital height) cap height of the font (os2.sCapHeight) Unused Unused Unused ?? Unused
subscriptShiftDown σ16, σ17 os2.ySubscriptYOffset 150/430.556 x-height for msub and 247.217/430.556 x-height ⅓ x-height Same as WebKit ?? os2.ySubscriptYOffset
subscriptTopMax ⅘σ5 ⅘ x-height ⅘ x-height ⅘ x-height Same as WebKit ?? ⅘ x-height
subscriptBaselineDropMin σ22 None 50/430.556 x-height ½ x-height Same as WebKit ?? ??
superscriptShiftUp σ13, σ14 os2.ySuperscriptYOffset 412.892/430.556 x-height in display mode and scriptlevel 0, 362.892/430.556 x-height otherwise x-height Same as WebKit ?? os2.ySuperscriptYOffset
superscriptShiftUpCramped σ15 None 288.889/430.556 x-height Unused Unused ?? ??
superscriptBottomMin ¼σ5 ¼ x-height ¼ x-height ¼ x-height Same as WebKit ?? ¼ x-height
superscriptBaselineDropMax σ18 None 386.108/430.556 x-height ½ x-height Same as WebKit ?? ??
subSuperscriptGapMin 4ξ8 4 × default rule thickness 4 × rule thickness 1/5 em Same as WebKit ?? 4 × rule thickness
superscriptBottomMaxWithSubscript ⅘σ5 ⅘ x-height ⅘ x-height ⅘ x-height Same as WebKit ?? ⅘ x-height
spaceAfterScript \scriptspace 0.5pt for a 12pt font. 0.5pt 1/5 em Same as WebKit ?? ??
upperLimitGapMin ξ9 None 111.111/430.556f x-height 3 × rule thickness Unused ?? ??
upperLimitBaselineRiseMin ξ11 None 200/430.556f x-height 0 Unused ?? ??
lowerLimitGapMin ξ10 None 166.667/430.556f x-height 3 × rulethickness Unused ?? ??
lowerLimitBaselineDropMin ξ12 None 600/430.556f x-height 0 Unused ?? ??
stackTopShiftUp σ10 None 443.731/430.556 x-height 0 Unused ?? ??
stackTopDisplayStyleShiftUp σ8 None 676.508/430.556 x-height 0 Unused ?? ??
stackBottomShiftDown σ12 None 344.841/430.556 x-height 0 Unused ?? ??
stackBottomDisplayStyleShiftDown σ11 None 685.951/430.556 x-height 0 Unused ?? ??
stackGapMin 3ξ8 3 × default rule thickness 3 × rule thickness 3 × rule thickness Unused ?? 3 × rule thickness
stackDisplayStyleGapMin 7ξ8 7 × default rule thickness 7 × rule thickness 7 × rule thickness Unused ?? 7 × rule thickness
stretchStackTopShiftUp ξ11 None Unused 0 Unused ?? ??
stretchStackBottomShiftDown ξ12 None Unused 0 Unused ?? ??
stretchStackGapAboveMin ξ9 Same value as upperLimitGapMin Unused 3 × rule thickness Unused ?? ??
stretchStackGapBelowMin ξ10 Same value as lowerLimitGapMin. Unused 3 × rule thickness Unused ?? ??
fractionNumeratorShiftUp σ9 None 393.732/430.556 x-height 0 Same as WebKit ?? ??
fractionNumeratorDisplayStyleShiftUp σ8 Same value as stackTopDisplayStyleShiftUp 676.508/430.556 x-height 0 Same as WebKit ?? ??
fractionDenominatorShiftDown σ12 None 344.841/430.556 x-height 0 Same as WebKit ?? ??
fractionDenominatorDisplayStyleShiftDown σ11 Same value as stackBottomDisplayStyleShiftDown 685.951/430.556 x-height 0 Same as WebKit ?? ??
fractionNumeratorGapMin ξ8 default rule thickness rule thickness + 1px rule thickness Same as WebKit ?? rule thickness
fractionNumDisplayStyleGapMin 3ξ8 3 × default rule thickness 3 × rule thickness 3 × rule thickness Same as WebKit ?? 3 × rule thickness
fractionRuleThickness ξ8 default rule thickness rule thickness rule thickness Same as WebKit ?? rule thickness
fractionDenominatorGapMin ξ8 default rule thickness rule thickness + 1px rule thickness Same as WebKit ?? rule thickness
fractionDenomDisplayStyleGapMin 3ξ8 3 × default rule thickness 3 × rule thickness 3 × rule thickness Same as WebKit ?? 3 × rule thickness
skewedFractionHorizontalGap ?? None Unused Unused Unused ?? Unused
skewedFractionVerticalGap ?? None Unused Unused Unused ?? Unused
overbarVerticalGap 3ξ8 3 × default rule thickness Unused 3 × rule thickness Same as WebKit ?? 3 × rule thickness
overbarRuleThickness ξ8 default rule thickness Unused Unused Unused ?? Unused
overbarExtraAscender ξ8 default rule thickness Unused rule thickness Same as WebKit ?? rule thickness
underbarVerticalGap 3ξ8 3 × default rule thickness Unused 3 × rule thickness Same as WebKit ?? 3 × rule thickness
underbarRuleThickness ξ8 default rule thickness Unused Unused Unused ?? Unused
underbarExtraDescender ξ8 default rule thickness Unused rule thickness Same as WebKit ?? rule thickness
radicalVerticalGap 5/4 ξ8 1¼ default rule thickness 5/4 rule thickness 5/4 rule thickness Same as WebKit ?? 5/4 rule thickness
radicalDisplayStyleVerticalGap ξ8 + ¼σ5 default rule thickness + ¼ x-height rule thickness + ¼ x-height rule thickness + ¼ x-height Same as WebKit ?? rule thickness + ¼ x-height
radicalRuleThickness ξ8 default rule thickness rule thickness rule thickness Same as WebKit ?? rule thickness
radicalExtraAscender ξ8 same value as radicalRuleThickness 0.2em rule thickness Same as WebKit ?? rule thickness
radicalKernBeforeDegree Hardcoded in root macro (e.g. 5/18 em) None Special adjustment if missing 5/18 em Same as WebKit ?? ??
radicalKernAfterDegree Hardcoded in root macro (e.g. −10/18 em) −10/18 of em −1.35 x-height −10/18 em Same as WebKit ?? −10/18 em
radicalDegreeBottomRaisePercent Hardcoded in root macro (e.g. .6) 60% 0.6 0.6 Same as WebKit ?? .6