code: function keyframe() {
          whitespace();
  
          const vals = [];
          let m;
  
          while ((m = match(/^((\d+\.\d+|\.\d+|\d+)%?|[a-z]+)\s*/))) {
              vals.push(m[1]);
              match(/^,\s*/);
          }
  
          if (vals.length) {
              return {
                  type        : 'keyframe',
                  values      : vals,
                  declarations: declarations()
              };
          }
      }
docs: Keyframes -------------------------------------------------------------------------