docs: highlighters should use _zsh_highlight_add_highlight

docs/highlighters.md

@@ -64,12 +64,17 @@ To create your own `myhighlighter` highlighter:
         }
 
 * Implement the `_zsh_highlight_myhighlighter_highlighter` function.
-  This function does the actual syntax highlighting, by modifying
-  `region_highlight`, for example:
+  This function does the actual syntax highlighting, by calling
+  `_zsh_highlight_add_highlight` with the start and end of the region to
+  be highlighted and the `ZSH_HIGHLIGHT_STYLES` key to use. Define the default
+  style for that key in the highlighter script outside of any function with `:
+  ${ZSH_HIGHLIGHT_STYLES[key]:=value}`. For example:
+
+        : ${ZSH_HIGHLIGHT_STYLES[aurora]:=fg=green}
 
         _zsh_highlight_myhighlighter_highlighter() {
-          # Colorize the whole buffer with blue background
-          region_highlight+=(0 $#BUFFER bg=blue)
+          # Colorize the whole buffer with the 'aurora' style
+          _zsh_highlight_add_highlight 0 $#BUFFER aurora
         }
 
 * Activate your highlighter in `~/.zshrc`: