anchor.diff:    ///  * <https://docs.microsoft.com/en-us/typography/opentype/spec/features_ae#case>
     const FontFeature.caseSensitiveForms() : feature = 'case', value = 1;
   
  -  // cvXX
     /// Select a character variant. (`cv01` through `cv99`)
     ///
     /// Fonts may have up to 99 character variant sets, numbered 1
  
positive.code:   /// * `decoration`: The decorations to paint near the text (e.g., an underline).
    /// * `decorationColor`: The color in which to paint the text decorations.
    /// * `decorationStyle`: The style in which to paint the text decorations (e.g., dashed).
    /// * `decorationThickness`: The thickness of the decoration as a muliplier on the thickness specified by the font.
    /// * `fontWeight`: The typeface thickness to use when painting the text (e.g., bold).
    /// * `fontStyle`: The typeface variant to use when drawing the letters (e.g., italics).
    /// * `fontFamily`: The name of the font to use when painting the text (e.g., Roboto). If a `fontFamilyFallback` is
  
negative.code:   /// broken top line in Traditional Chinese, but a solid top line in
    /// Simplified Chinese, Japanese, Korean, and Vietnamese. This kind
    /// of variation also exists with other alphabets, for example
    /// Cyrillic characters as used in the Bulgarian and Serbian
    /// alphabets vary from their Russian counterparts.
    ///
    /// A particular font may default to the forms for the locale for
  