demo · v134 · css

Font Glyph Lab

Authors a live @font-feature-values rule, applies it to a sample, and reads the rule back out of the stylesheet using the newly-exposed CSSFontFeaturesValueRule interface — proof you can now programmatically introspect what you just wrote.

Toggle feature aliases and apply them to the sample below. The generated @font-feature-values block is what we round-trip through CSSOM.



    

      
Type & Glyphs: handcrafted.

    


    
read back via CSSOM

    

      
feature aliastypenameresolved value(s)

      
— not read yet —

    

    
  


  

    
before vs after

    
Before v134: window.CSSFontFeaturesValueRule was undefined. To find a font-feature-values rule, tooling had to walk document.styleSheets, fish out rules whose cssText started with @font-feature-values, then regex-parse the body. Brittle.

    
After v134: the IDL is exposed. rule instanceof CSSFontFeaturesValueRule works, you can read rule.fontFamily and the alias maps directly.

  


  

    
see also