anchor.diff:   ** allow image to span width of page (role=canvas, role=canvas-x or role=canvas-y); if role is canvas or canvas-y, then it does not consume height
    ** partially addressed by vw units
   * 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?
  - ** separate theme control for listing vs literal block (and maybe source too)
  + ** actually, this has to do with the a miscalculation in dry run when not starting from same y position
  +* 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)
   * add feature to number bullets according to section number (needed for OpenDevise agreements)
    ** allow ordered list marker to be prefixed by section number (a global setting?)
  
positive.code: * don't create title page for article doctype (#95, #105)
   ** 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
   ** intended primarily for image slideshows
   ** this is slighly more complicated now that we have mirror margins; perhaps can't set those from document?
  
negative.code: * height of listing block not calculated correctly when string of contiguous characters exceeds length of line
   ** put listing block with very long line inside of sidebar; see that sidebar height is incorrect (too large)
   ** is this because source highlighting is not done in scratch document?
  * add line swell when drawing dashed line on listing block
  * rework resolve_image_path API so it's more logical; override based on type of first argument; document as option
  * rename text-alignment attribute to text-align? (change is within alpha.14, so still a chance to change)
  * report cursor / bounding box bug in column_box
  