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]
  +http://www.gradle.org/docs/current/javadoc/org/gradle/api/tasks/util/PatternSet.html[PatternSet]
   
   [source,groovy]
   .build.gradle
  
positive.code: 
  Some backends require that additional files be copied across. The most common example are images for HTML backends. For
  this the `resources` method is used. It is provided with a closure that configures an internal
  {http://www.gradle.org/docs/current/javadoc/org/gradle/api/file/CopySpec.html}[CopySpec]
  
  [source,groovy]
  .build.gradle
  
negative.code:   Type: File, but any object convertible with `project.file` can be passed.
    Default: `src/docs/asciidoc`.
  sources:: specify which Asciidoctor source files to include by using an
    http://www.gradle.org/docs/current/javadoc/org/gradle/api/tasks/util/PatternSet.html[Ant-style PatternSet].
  resources:: specify which additional files (image etc.) must be copied to output directory using a
    http://www.gradle.org/docs/current/javadoc/org/gradle/api/file/CopySpec.html[CopySpec].
  outputDir:: where generated docs go.
    Use either `outputDir path`, `setOutputDir path` or `outputDir=path`
    Type: File, but any object convertible with `project.file` can be passed.
  