anchor.diff:  
   == TODO
   
  +* add bw / grayscale theme for rouge
   * fix labels in issue tracker to match other projects; in particular, enhancement should be green.
   * setup asciidoctor-mathoid project, then mention it in the STEM support section
   * QUESTION should we show keys with hyphens instead of underscores in theming guide?
  +* add preamble to toc
   
   .1.5.0.alpha.17
  +* don't need to use symbols with alias
  +* document rouge-style in README (already in theming guide, but gets buried)
  +* pass current styles downwards when parsing formatted text (see https://github.com/asciidoctor/asciidoctor-pdf/issues/854)
   * test suite
   * start the README with a proper introduction to Asciidoctor PDF (and not so focused on Prawn)
   * support unnumbered and no-bullet style on ordered list
    ** see https://github.com/asciidoctor/asciidoctor/pull/2286
  -* remove hack to add trailing endline to source for rouge (now fixed in rouge)
  - ** set minimum rouge version
   * implement SVG fit for background image (#765)
   * add helper to expand value into 4 coordinates (top, right, bottom, left)
   
  
positive.code:  ** probably need to introduce a model object to hold the cache
  * line height in TOC is too small if heading only contains monospaced text
  * UPSTREAM: rouge treats a CSS property as a Name::Label instead of a Keyword (see https://github.com/jneen/rouge/issues/665)
  * UPSTREAM: rouge incorrectly identifies an endline in a schemaLocation attribute in XML as an error (see https://github.com/jneen/rouge/issues/663) (PR sent)
  * FIXME: stop using fallback fonts in default theme (instead, bundle a fuller font)
   ** using fallback fonts significantly slows down Prawn because it checks every letter every time (see https://github.com/prawnpdf/prawn/blob/master/lib/prawn/text/formatted/box.rb#L427-L434)
   ** add broader character range to monospace font so we can drop fallback font by default (#282)
  
negative.code: * Prawn reports unknown blank font if family is valid but style is invalid (see https://github.com/prawnpdf/prawn/issues/1022)
  * catch UnsupportedImageType and issue warning that suggests using prawn-gmagick; see sandbox/interlaced.png
  * something like prawn-gmagick in Java env
   ** look into https://github.com/jcupitt/ruby-vips for faster image processing (might solve our JRuby issue)
  * look for image in imagesoutdir if set and the image cannot otherwise be resolved
  * in follow-up to #271, mention that images are resolved at the time of conversion; thus, they need to be located where the converter can find them; that often means setting imagesdir to an absolute path
  * split out the background fill from PR 664 into a separate PR to merge sooner
  