anchor.diff:    - document unicode values
     - document how to load theme (with special attention to fonts & images)
     - positional meanings of array items
  +* images
  +  - multiple image width by 0.75 to get point value
  +  - should we use native size of image by default? (after multiplying by 0.75)
  +* implement stem support
  +* rethink how we are handling line heights for fonts, then document carefully
   * dedicated style for top/bottom margin of outline list
   * need dedicated theme styles for paragraph spacings, etc
   * can't put margin top on chapter (chapter_top?)
  
positive.code: * theme idea / tester: see sandbox/ebook-learn_version_control_with_git-SAMPLE.pdf
  * make alternating page title position optional (via theme?)
  * BUG: page numbers are off in Clojure Cookbook
  * image in header / banner (need to implement a masthead)
  * fix passthrough placeholders that get caught up in syntax highlighting (see https://github.com/asciidoctor/asciidoctor/blob/master/test/blocks_test.rb#L2258-L2277)
  * we could eliminate some of the tags we're currently matching in the formatted text parser (e.g., link)
  * add Preamble to TOC
  
negative.code: 
  * source highlighting (with Pygments) not working inside an admonition block (see chronicles.adoc)
    - *don't need to run source highlighter in dry run*
  * getting a line wrap break before comma if preceding word is emphasized (problem in Prawn wrapping)
  * don't create blank page first page if content overflows and we're on the first page (already fixed?)
  * toc
    - make dot leader style separate from title / number
  * running content
  