wpf - How does IDataErrorInfo.this[string propertyName] work in C#? -

I have always implemented the interface to think exactly what this line means and how it works.

  string IDataErrorInfo.this [string propertyName] {receive {this return.GetValidationError (propertyName); }}   
 How does  .this [string propertyName]  work, and when / how is this property called?   
 
 
  this [key]  is actually an indicator, and some assets and There is a cross between a method, it works like a property because you can tie it, but unlike regular properties, it receives a parameter.  
 Behind the scenario, it has been implemented as a method -  get_Item (key) , and if you want to access it through reflection, For example:  
  Typhus (Myclass) .GetProperty ("item"); It is also important to know when implementing   
  INotifyPropertyChanged , in that case,  "item []"  or  binding.    IndexerName  should be used as the property name.