anchor.diff:    - Color as hex string (e.g., #ffffff)
     - Image path
     - Enumerated type (where specified)
  +  - Text content (where specified)
   * Null (clears any previously assigned value)
     - _empty_ (i.e., no value specified)
     - null
  
positive.code:     columns: <50% =0% <50%
  
  |<side>_<position>_content^[3,4]^
  |Quoted string
  |footer:
    verso:
      center:
  
negative.code: title_page:
    logo_image: image:logo.png[width=250,align=center] 
  ----
  
  === Quoted String
  
  Some of the keys accept a quoted string as text content.
  The final segment of these keys is always named `content`.
  
  A content key accepts a string value.
  It's usually best to quote the string or use the http://symfony.com/doc/current/components/yaml/yaml_format.html#strings[YAML multi-line string syntax].
  
  Text content may be formatted using a subset of inline HTML.
  You can use the well-known elements such as `<strong>`, `<em>`, `<code>`, `<a>`, `<sub>`, `<sup>`, `<del>`, and `<span>`.
  The `<span>` element supports the `style` attribute, which you can use to specify the `color`, `font-weight`, and `font-style` CSS properties.
  You can also use the `rgb` attribute on the `<color>` element to change the color or the `name` and `size` attributes on the `<font>` element to change the font properties.
  If you need to add an underline or strikethrough decoration to the text, you can assign the `underline` or `line-through` to the `class` attribute on any aforementioned element.
  
  Here's an example of using formatting in the content of the menu caret:
  
  [source,yaml]
  ----
  menu_caret_content: " <font size=\"1.15em\"><color rgb=\"#b12146\">\u203a</color></font> "
  ----
  
  Additionally, normal substitutions are applied to the value of content keys for <<Running Content (Header & Footer),running content>>, so you can use most AsciiDoc inline formatting (e.g., `+*strong*+` or `+{attribute-name}+`) in the values of those keys.
  
  == Fonts
  
  