anchor.diff:  * use term "page number label" to refer to the visible, printed page number (not the implicit page number)
   * vertical alignment of text doesn't work properly in Prawn; better to calculate alignment manually, if possible
   
  +== Snippets
  +
  +Report error eagerly if can't read image in running content:
  +
  +```
  +warn %(asciidoctor: WARNING: could not embed image in running content: #{path}; #{e.message})
  +side_content[position] = %([#{attrs['alt'] || (::File.basename path, (::File.extname path)).tr('_-', ' ')}]
  +```
  +
   == Prawn Wishlist
   
   * fragment should be able to specify it's own width
  
positive.code: * cache stateless cell data resolved from theme (don't need to recalc each time; at least per table)
  * FILE ISSUE: autowidth on table doesn't work for multi-line content (prawn-table bases width calculation on normalized value)
    - table ends up being stretched even though it doesn't need to be
  * table logic: does the layout_table_caption have to be inside the table block? can we pre-calculate the actual width for the caption? does the table offer a callback we can use to keep the caption on the same page as the table?
  * introduce object to store/organize running content data and specs
  * QUESTION: should theme font handle hierarchical keys (either explicitly or implicitly)
  
negative.code: * theme idea / tester: see sandbox/ebook-learn_version_control_with_git-SAMPLE.pdf
  * make alternating page title position optional (via theme?)
  * fix passthrough placeholders that get caught up in syntax highlighting (see https://github.com/asciidoctor/asciidoctor/blob/master/test/blocks_test.rb#L2258-L2277)
  * honor font defs in SVG (to get M+ 1p); prawn-svg supports loading fonts; need to pass fonts to prawn-svg
  * should we support % as a unit in theme (divides by 100 and sets float value)?
  * disable monospace font color (and family?) in headings
  