anchor.diff:  - default
   - ./brand-theme.yml
   |===
  +
  +=== Extending the Font Catalog
  +
  +If you define a <<Custom fonts,font catalog>> in a theme that extends from `default`, and you want to continue to use the bundled fonts in your theme, you either have to redeclare the bundled fonts:
  +
  +.Redeclaring the bundle fonts in a custom theme
  +[source,yaml]
  +----
  +extends: default
  +font:
  +  catalog:
  +    Noto Serif:
  +      normal: GEM_FONTS_DIR/notoserif-regular-subset.ttf
  +      bold: GEM_FONTS_DIR/notoserif-bold-subset.ttf
  +      italic: GEM_FONTS_DIR/notoserif-italic-subset.ttf
  +      bold_italic: GEM_FONTS_DIR/notoserif-bold_italic-subset.ttf
  +    M+ 1mn:
  +      normal: GEM_FONTS_DIR/mplus1mn-regular-subset.ttf
  +      bold: GEM_FONTS_DIR/mplus1mn-bold-subset.ttf
  +      italic: GEM_FONTS_DIR/mplus1mn-italic-subset.ttf
  +      bold_italic: GEM_FONTS_DIR/mplus1mn-bold_italic-subset.ttf
  +    Your Font:
  +      normal: /path/to/your/font.ttf
  +heading:
  +  font-family: Your Font
  +----
  +
  +or you need to set `merge: true` above your font definitions:
  +
  +.Merging with the inherited font catalog
  +[source,yaml]
  +----
  +extends: default
  +font:
  +  catalog:
  +    merge: true
  +    Your Font:
  +      normal: /path/to/your/font.ttf
  +heading:
  +  font-family: Your Font
  +----
  +
  +If you're referring to a bundled font, you'll need to prefix the path with `GEM_FONTS_DIR` (or add it to the value of the `pdf-fontsdir` attribute) so the converter can find and register it.
  +You can find the bundle font definitions in default theme.
   
   [#keys-role]
   === Role
  
positive.code: Topics remaining to document:
  * line height and line height length (and what that all means)
  * title page layout / title page images (logo & background)
  * document that unicode escape sequences can be used inside double-quoted strings
  ////
  
  [.lead]
  The theming system in Asciidoctor PDF is used to control the layout and styling of the PDF file Asciidoctor PDF generates from AsciiDoc.
  This document describes how the theming system works, how to define a custom theme in YAML and how to activate the theme when running Asciidoctor PDF.
  
  TIP: The quickest way to create your own theme is to <<Extends,extend the default theme>>.
  This not only gives you a set of foundation styles to build on, it also provides a collection of <<Bundled Fonts,bundled fonts>>.
  If you want to replace the bundled fonts with your own, you must declare the name and location of each font in the <<Custom Fonts,font catalog>>.
  To reuse the bundled fonts, you can either extend the default theme and/or redeclare the bundled fonts in the font catalog.
  
  WARNING: If you don't declare your own fonts (or extend the default theme), only the built-in (AFM) fonts provided by the PDF reader will be available.
  Using AFM fonts can result in missing functionality and warnings.
  See the <<Built-In (AFM) Fonts>> section to learn more about these limitations.
  
  
negative.code: If the filename begins with `./`, it's resolved as a theme file relative to the current theme file.
  Otherwise, the filename is resolved as a theme file in the normal way (relative to the value of the `pdf-themesdir` attribute).
  
  Currently, the base theme is always loaded first.
  Then, the files referenced by the extends key are loaded in order.
  Finally, the keys in the current file are loaded.
  