anchor.diff:  
   |text-decoration-width
   |<<values,Number>> +
  -(default: 1)
  +(default: $base-text-decoration-width)
   |role:
     underline:
       text-decoration-width: 0.5
  
positive.code: 
  |text-decoration-width
  |<<values,Number>> +
  (default: 1)
  |link:
    text-decoration-width: 0.5
  |===
  
negative.code: 
  |text-decoration-width
  |<<values,Number>> +
  (default: $base-text-decoration-width)
  |toc:
    text-decoration-width: 0.5
  
  