Current Scope Highlighting
Current Scope feature enables you to see current parentheses and hierarchy scope when you navigate through the code highlighting active bracket pairs and structures.
The current scope feature also enables error highlighting (in red color) of mismatched brackets.
To better indicate range of the current scope, outlining margin against of the current scope can be highlighted in different color (so current outlining area). On default schema it is just more intensive (darker) color of the standard outlining, but can be customized as you like (fore and back color) in Fonts and Colors settings by changing style Outlining (Highlighted).
You can enable the feature in Options->Code Completion.