code: void removeMixin() {
          int idx = state.stackIdx - 1;
          Scope current = state.stack.get( idx );
          if( idx > 0 ) {
              Scope previous = state.stack.get( idx - 1 );
              Map<String, Expression> currentReturn = previous.returns;
              Map<String, Expression> vars = current.variables;
              if( vars != null ) {
                  for( Entry<String, Expression> entry : vars.entrySet() ) {
                      if( previous.getVariable( entry.getKey() ) == null ) {
                          currentReturn.put( entry.getKey(), ValueExpression.eval( this, entry.getValue() ) );
                      }
                  }
              }
              vars = current.returns;
              if( vars != null ) {
                  for( Entry<String, Expression> entry : vars.entrySet() ) {
                      if( previous.getVariable( entry.getKey() ) == null ) {
                          currentReturn.put( entry.getKey(), ValueExpression.eval( this, entry.getValue() ) );
                      }
                  }
              }
          }
          state.stackIdx--;
          state.rulesStackModCount++;
      }
docs: Remove the scope of a mixin.