anchor.diff:          h3 They also allow 2 way message passing between the generator function and the calling code
   
         section
  -        h1 Generators
  +        h2 Generators
           pre
             code.language-javascript.
               function *gen() {
  
positive.code: 
        section(data-bespoke-hash="async")
          h1 Async
  
        section(data-bespoke-hash="stage2")
          h1 Stage 2
  
negative.code:             it.next(); // {value: undefined, done: true}
  
        section
          h2 Generators
          pre
            code.language-javascript.
              function *fib() {
  