anchor.diff:  
   == TODO
   
  +* use background color from pygments theme for source block
  +* what should we set as the border color if the source highlighting theme has a background color?
  +* height of listing block not calculated correctly when string of contiguous characters exceeds length of line
  +  - put listing block with very long line inside of sidebar; see that sidebar height is incorrect (too large)
  +  - is this because source highlighting is not done in scratch document?
   * backport resize method from prawn-svg and use it in converter (now in two places)
   * rework resolve_image_path API so it's more logical; override based on type of first argument; document as option
   * rename text-alignment attribute to text-align? (change is within alpha.14, so still a chance to change)
  
positive.code: * introduce theme keys for styling index
  * index term that wraps should have a hanging indent (#645)
  * rename inherited_align to text_align? (and base_align to base_text_align?)
  
  * allow front cover and back cover image to be defined in theme as fallback; document in theming-guide
  * FILE ISSUE only nest document outline inside root node if doctype=article
  * don't crash if image in running content is an unsupported format
  * support image URL (using resolve_image_path) in running content (what about data-uri?)
  
negative.code:   - currently controlled by theme
  * make conum glyphs configurable in theme (use reference table to resolve)
  * CJK and/or multilingual support (see https://github.com/chloerei/asciidoctor-pdf-cjk)
    - document this in the README
  * description list term should keep together with content (file issue)
  * allow font properties to be set for lists (description_list, outline_list)
  * hardbreak in table cell results in extra endline (likely not normalizing cell content)
  