https://learn.microsoft.com/en-us/dotnet/api/microsoft.visualstudio.text.tagging.ierrortag.tooltipcontent?view=visualstudiosdk-2022
IErrorTag.ToolTipContent Property (Microsoft.VisualStudio.Text.Tagging) | Microsoft Learn
Gets the content to use when displaying a tooltip for this error. This property may be null.
propertymicrosoftvisualstudiotexttagging