anchor.diff:  the user interface:
   
   *Default*::
  -    Default colors:::
  +    default colors:::
           The default foreground and background colors. If the value of *default*
           is used here, then the colors used will be your terminal's defaults.
   
  
positive.code:             *white* *bright-black*, *bright-red*, *bright-green*,
              *bright-yellow* *bright-blue*, *bright-magenta*, *bright-cyan*,
              *bright-white*
         The existing color:::
              *default*
          A hexadecimal value:::
              *rgb:RRGGBB*, *rgba:RRGGBBAA*
      If left unspecified, the value of *default* is used.
      Alpha values are used to blend the face onto either its base (see below) or
      else onto whatever color happens to be used at the moment. For technical
      reasons, alpha values must be >16.
  
  attributes::
      A string whose individual letters each set an attribute:
          *u*:::
              Underline
          *c*:::
              Curly underline
              Note: This takes precedence over underline if both are specified.
          *r*:::
              Reverse
          *b*:::
              Bold
          *B*:::
              Blink
          *d*:::
              Dim
          *i*:::
              Italic
          *s*:::
              Strikethrough
          *F*:::
              Final::::
                  Override the previous face instead of merging with
                  it. Can only be replaced if another face with the final
                  attribute is applied.
          *f*:::
              Final foreground::::
                  Same as final, but only applies to a face's foreground color.
          *g*:::
              Final background::::
                  Same as final, but only applies to a face's background color.
          *a*:::
              Final attributes::::
                  Same as final, but only applies to a face's attributes.
  
  base::
      The face onto which the rest of the face applies. Its value can be any
      face name, as long as no cycle is introduced. A face can reference itself,
      in which case it will apply on top of the parent scope.
  
  == Built-in faces
  
  
negative.code: echo -markup 'default {Error}error{Default} default'
  ----
  
  Inside a markup string, a literal `{` character is written as `\{`, and a
  literal backslash (`\`) character is written as `\\`.
  
  The `{\}` string disables markup processing for the rest of the line. It
  can be used to avoid having to escape text that might be mistaken for markup
  