C# XML /// Comments, where does tag show up?

When you see the method in View >> Object Browser

For e.g. you will see something like this:

private int GetColumnIndex(Microsoft.Office.Interop.Excel.Worksheet worksheet, string columnName, int rowIndex, int startColumnIndex)
    Member of MyAddIn.CommandHandlers.CommandHandler

Summary:
Returns the column index with specified name and in specified row

Parameters:
worksheet: Target worksheet
columnName: Column name to find
rowIndex: Row index in which to search the column
startColumnIndex: Start index of the column

Returns:
The index of column if found, else returns 0