anchor.diff:  It can also be used to add an entry to the TOC for a preamble, anonymous preface, and imported PDF pages.
   See xref:notitle.adoc[] for examples and more details.
   
  +[#blocks]
   == Blocks and block captions
   
  -Blocks and block captions gained a lot of new features in Asciidoctor PDF 2.0.
  -Here are just a few of the highlights:
  -
  -Smart bottom margins::
  -Blocks now have smarter bottom margins that prevent extra space from being added below them, particularly when blocks are nested or used inside an AsciiDoc table cell.
  +Blocks and block captions gained a lot of new theming capabilities in Asciidoctor PDF {page-component-version}.
  +Here are a few of the highlights:
  +
  +Padding::
  +The theme can now control the padding on a block using a 2-value array for ends and sides or 3-value array with implied left side value.
   Border width::
   The border width of delimited blocks, admonitions, and block images can be customized per edge with the xref:theme:blocks.adoc#border-width[border-width key].
   Border style::
  
positive.code: The `unbreakable` option can be applied to all delimited blocks (including admonitions and tables), but not sections.
  When the xref:breakable-and-unbreakable.adoc#unbreakable[unbreakable option] is applied to a block, the converter will advance the block and its caption and anchor to the next page if it detects that the block would break across pages and it can fit on a single page.
  
  == Notitle option
  
  The `untitled` option has been renamed to `notitle`.
  
negative.code: The new theme keys let you customize the font properties, text alignment, and item spacing of callout lists.
  The `callout-list` category includes the `margin-top-after-code` key that can control the top margin of callout lists that immediately follow a code block.
  
  .*_Notable fixes for callouts_*
  * Callout numbers in a callout list stay with primary text when an item is advanced to the next page.
  * A sequence of two or more callouts separated by spaces in a code block are processed correctly.
  * The font family assigned to `conums` in the theme is applied to the callout numbers displayed in code blocks.
  