anchor.diff:  * add support for nested tables by writing custom Table::Cell implementation
   * add support for footnotes (as article or chapter endnotes)
   * rework text handling in Prawn to support line height natively
  +* margin collapsing (like CSS)
   
   == Documentation
   
  
positive.code: * need some sort of post_construct method for converter that receives document
    - inline convert methods can get called before init_pdf
    - monkeypatch?
  * backport resize method from prawn-svg and use it in converter
  * create document that explains how built-in fonts are generated and what subsets are selected
    - I need instructions for myself so I know how to update/modify the fonts
    - document in theming guide what must be done to prepare fonts (old-style 'kern' table, optionally subset) (file issue!)
  * consider supporting icon tag in parser to simplify how inline icons are stored; simpler use of passthrough content
  * cache stateless cell data resolved from theme (don't need to recalc each time; at least per table)
  * 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)
  * need to support .canvas role on image so it isn't shrunk to fit inside top/bottom margins
    - perhaps .canvas, .canvas-x, .canvas-y
  * FILE ISSUE: when split source listing, add top padding to bounding box (or is it the line metrics top?)
    - perhaps this has to do with the a miscalculation in dry run when not starting from same y position?
  * should we print alt text if an error is caught when attempting to embed an image?
  * stroke and fill multi-page sidebar block (#259) and example block (#362)
  * support URL images in running content (need to delegate to resolve_image_path)
  
negative.code:   - only create title page if doctype=book
  * allow character spacing to be controlled by theme
  * might be able to avoid dry run for listing/literal in obvious cases; engineering estimate
  * allow pdf-page-margin to be set in document
    - this is slighly more complicated now that we have mirror margins; perhaps can't set those from document?
  * use `module Asciidoctor; module PDF; module FormattedText` convention to simplify indentation
  * introduce code style guide (like in Jekyll AsciiDoc); perhaps make this a shared file in the Asciidoctor ecosystem?
  * I'd like for theme to be able to set font scan path for Prawn SVG, but registry is global
  * rename dot_leader to just leader or tab_leader?
  * rename align to text_align?
  * QUESTION should bullets be on right if list alignment is right (what about center?)
  * QUESTION should we resolve font-based icons globally, in init_pdf?
  
  * use treetop to parse and evaluate theme file
  * use or don't use pad method? check performance
  * switch wolpertinger to howling grasshopper mouse
  
  == Major Efforts / Milestones
  
  