anchor.diff:  * .ad
   
   To select only certain files use the `sources` method. This takes a closure which in turn configures an internal
  -http://www.gradle.org/docs/current/javadoc/org/gradle/api/tasks/util/PatternSet.html[PatternSet]
  -
  -[source,groovy]
  -.build.gradle
  -----
  -sources {
  -  include 'toplevel.adoc'
  +http://www.gradle.org/docs/current/javadoc/org/gradle/api/tasks/util/PatternSet.html[PatternSet].
  +
  +To specify a custom output folder, use the `outputDir` method.
  +
  +[source,groovy]
  +.build.gradle
  +----
  +asciidoctor {
  +  sourceDir = file('docs')
  +  sources {
  +    include 'toplevel.adoc', 'another.adoc', 'third.adoc'
  +  }
  +  outputDir = file('build/docs')
   }
   ----
   
  
positive.code: used as option values, otherwise the Ruby runtime will throw an exception.
  
  Notice how spaces are escaped in the last key/value pair.
  
negative.code: 
  === Defining Sources
  
  The plugin will search for sources under `sourceDir`. Sources may have any of the following extensions in
  order to be discovered:
  
  * .asciidoc
  