anchor.diff:    - later on, initialize_wrap drops fragment with empty text
   * use term "page number label" to refer to the visible, printed page number (not the implicit page number)
   
  +== Known Issues
  +
  +* inline image at start of the line is slighly shifted to the right due to the fact that it's placed in the center of the reserved fragment width; perhaps we are adding this padding
  +
   == Potential Optimizations
   
   * if autofit is set on a listing/literal block that has conums, we are splitting fragments by line twice
  
positive.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)
  * add Preamble to TOC
  * NOTE prawn-svg supports loading from a URI (only applies to embedded images); does it work in Asciidoctor PDF?
  * 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 color in headings
  * add source language to upper-left corner of listing block
  
  * implement quote style from default Asciidoctor stylesheet
  
negative.code: * **allow theme_font to set line_height** (honor this setting from document)
    - theme setting for code line height (currently using base_line_height)
  * should we put an entry for doctitle in the outline if notitle is set? (need to test these edge cases)
  * add more theme control over toc (font size, style, color per level)
  * don't allow formatted text (e.g., monospace) in headings or toc entries
  * prevent title-logo-image from spilling to next page (same with title content)
  * document what each keep_together is doing / expects
    - keep_together really needs to pick up the inherited horizontal bounds or else measurement is inaccurate
  * code cleanups (regexps to constants, nil? checks and such)
    - split prawn_ext/extensions into individual files based on function
  * enable line above (or below?) title on title page (file issue)
    - perhaps 4-sided border?
  * enable text transform for:
    - running content
    - admonition content
    - table foot row
    - table header cell
    - table (overall)
    - generic paragraph?
    - inline literal text
    - link
    - listing/literal/source block
    - global default
  * file upstream issue for Prawn to warn if it can't resolve a glpyh (or monkeypatch it)
  * support web fonts; use uri-cache to avoid redundant fetching
  * align caption to match alignment of block image
  * FILE ISSUE: attribute or role to control table shading (all, even, odd) (or call it striped like bootstrap?)
    - e.g., [.striped]
    - currently controlled by theme
  * make conum glyphs configurable in theme (use reference table to resolve)
  * do we still need the converter hack in convert_content_for_block? (seems to be needed for admonitions)
  * utility to coerce the color value transparent to nil (better handling in general)
  * CJK and/or multilingual support (see https://github.com/chloerei/asciidoctor-pdf-cjk)
  * 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)
  * remove pdfmarks file after optimizing
  * add note to README that Prawn will subset any fonts provided
  * look into single_line + shrink_to_fit in listings, perhaps other places
  * refactor as Prawn view to avoid method name conflicts (also see https://github.com/prawnpdf/prawn/issues/802)
  * create proper default (Asciidoctor) theme
  * document how the treetop parser is rebuilt
  * rework font so we can set actual height, calculate x_height internally (use 1em for spacings)
  * padding top and bottom on content affects height_of calculations (need to review)
  * code font needs to support more than just ascii (Golo license block is an example)
  * don't cutoff content in partintro
  * admonition styles are one big hack; need to be organized and based on theme
  * FILE ISSUE: can't change font properties of admonition block content
  * SIMPLE: add admonition_label_font_color to theme
  * BUG: autofit logic not working with Courier (still overrunning line)
  * honor safe mode rules
  * print scratch.pdf file if verbose / trace mode is on in Asciidoctor
  * introduce setting to indent section content
  * rename default theme to docbook theme, make default the Asciidoctor theme (should we have a base theme?)
  * allow relative font size for inline code to be set (perhaps a percentage or em value? there are problems with this in arranger)
  * apply line height metrics for table content
    - figure out how to adjust line height for monospaced cell content
    - figure out how to layout regular cell content to adjust for line height
  