https://learn.microsoft.com/tr-tr/dotnet/api/system.windows.forms.datavisualization.charting.datapointcustomproperties.custompropertiesextended?view=netframework-4.8.1
DataPointCustomProperties.CustomPropertiesExtended Property...
Gets or sets the extended custom properties of the data point. Extended custom properties can be specified in the following format: AttrName1=Value1,...
property