anchor.diff:  
   [source,javascript]
   ----
  -var content = '== Title';
  -var doc = asciidoctor.load(content);
  +const content = '== Title';
  +const doc = asciidoctor.load(content);
   console.log(doc.getAttribute('data-uri')); // prints undefined
   console.log(doc.getAttribute('data-uri', 'false')); // prints 'false'
   
  
positive.code: const registryB = asciidoctor.Extensions.create();
  
  registryA.block(function () {
    var self = this;
    self.named('shout');
    self.onContext('paragraph');
    self.process(function (parent, reader) {
  
negative.code: 
  [source,javascript]
  ----
  const asciidoctor = require('asciidoctor.js')();
  asciidoctor.Extensions.register(function () {
    this.block(function () {
      const self = this;
      self.named('shout');
      self.onContext('paragraph');
      self.process(function (parent, reader) {
        const lines = reader.getLines().map(function (l) { return l.toUpperCase(); });
        return self.createBlock(parent, 'paragraph', lines);
      });
    });
  