Finally found the answer. It was in Field Mapping logic for 9.2
"Here are the field mapping text parameters:
[Field Name] [Alias] [Editable] [IsNullable] [IsRequired] [Size] [Type]
[Precision] [Scale], [Merge Rule], [Delimiter], [Input Field Location, Input
Field Name], [Start Postion, End Postion], [Additional Input Field Location,
Input Field Name], [Start Postion, End Postion]
IsRequired is a hidden property and not assignable.
The booleans are the [Editable] [IsNullable] [IsRequired]
The recommended method by development is to use the field mapping object and not
the string."
A big thank you to the author, Dave Bollinger, and Simon Willis, whose link led me to it. I wish ESRI would document since I wanted to use fieldmappings, but could not find an example with append.