[MSDN Library April 2000] optional (100%)

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 Qualifiers (37.7021651117761%)

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

[MSDN Library April 2000] optional (31.4782608695652%)

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

[MSDN Library April 2000] Optional Fields (27.9814520402756%)

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 Message (23.8151223776224%)

MSDN Library - April 2000 > Windows Resource Kits > Windows 2000 Server Resource Kit > TCP/IP Core Networking Guide > Appendixes > DHCP Options > DHCP Extensions