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:   // Start of feature tag list.
    // ------------------------------------------------------------------------
  
    // aalt
    /// Access alternative glyphs. (`aalt`)
    ///
    /// This feature selects the given glyph variant for glyphs in the span.
    ///
    /// {@tool sample --template=stateless_widget}
    /// The Raleway font supports several alternate glyphs. The code
    /// below shows how specific glyphs can be selected. With `aalt` set
    /// to zero, the default, the normal glyphs are used. With a
  
negative.code:   ///
    /// This feature, when supported by the font, causes these glyphs to
    /// be shifted slightly, or otherwise adjusted, so as to form a more
    /// aesthetically pleasing combination with capital letters.
    ///
    /// {@tool sample}
    /// The Piazzolla font supports the `case` feature. It causes
    /// parentheses, brackets, braces, guillemets, slashes, bullets, and
    /// some other glyphs (not shown below) to be shifted up slightly so
  