anchor.diff:  
   We'll cover more about math expressions later.
   
  -==== Custom variables
  +==== Custom Variables
   
   You can define arbitrary key names to make custom variables.
   This is one way to group reusable values at the top of your theme file.
  
positive.code: . `<parity>` can be `odd` (odd rows) or `even` (even rows).
  
  [[key-toc]]
  === Table of contents
  
  The keys in this category control the arrangement and style of the table of contents.
  
  
negative.code: * https://github.com/asciidoctor/asciidoctor-maven-examples/tree/master/asciidoctor-pdf-with-theme-example[Maven Example]
  * https://github.com/asciidoctor/asciidoctor-gradle-examples/tree/master/asciidoc-to-pdf-with-theme-example[Gradle Example]
  
  == Theme-Related Document Attributes
  
  There are various settings in the theme you control using document attributes.
  These settings override equivalent keys defined in the theme file, where applicable.
  