code: private void findExpressionParameters(Expression expression, List<VariableInfo> parameters) {
      if (expression instanceof NameExpr) {
        NameExpr nameExpr = ((NameExpr) expression);
        if ("$event".equals(nameExpr.getNameAsString())) {
          processEventParameter(expression, nameExpr, parameters);
        } else {
          processNameExpression(nameExpr, parameters);
        }
      }
  
      expression
          .getChildNodes()
          .stream()
          .filter(Expression.class::isInstance)
          .map(Expression.class::cast)
          .forEach(exp -> findExpressionParameters(exp, parameters));
    }
docs: Find all the parameters this expression depends on. This is either the local variables (from a
  v-for loop) or the $event variable.
  
  @param expression An expression from the Template
  @param parameters The parameters this expression depends on