[MSDN Library April 2000] optional (54.5932678821879%)

MSDN Library - April 2000 > Platform SDK > Component Services > COM > Microsoft Interface Definition Language (MIDL) > MIDL Language Reference

[MSDN Library April 2000] optional (36.0969899665552%)

MSDN Library - April 2000 > Platform SDK > Component Services > COM > Automation > Type Libraries and the Object Description Language > ODL Reference > Attribute Descriptions

[MSDN Library April 2000] Optional Fields (22.2569533480349%)

MSDN Library - April 2000 > Platform SDK > Web Services > Internet Information Services SDK > Programmer's Guide > Reference > Internet Database Connector Reference > Internet Database Connector Fields

[MSDN Library April 2000] Optional Implementation (20.5214852891015%)

MSDN Library - April 2000 > Platform SDK > Networking and Directory Services > Active Directory, ADSI, and Directory Services > Active Directory Service Interfaces (ADSI) > Implementing ADSI Providers > Provider Minimum Requirements

[MSDN Library April 2000] Optional Qualifiers (20.3456827194881%)

MSDN Library - April 2000 > Platform SDK > Management Services > Windows Management Instrumentation > WMI Reference > WMI Standard Qualifiers