DerivativeSecurityListRequest/FIX.5.0SP1+

Message Content of DerivativeSecurityListRequest (MsgType=z)

TagText	FieldName or ComponentName	Required	Description
	StandardHeader	x	MsgType = z (lowercase Z)
320	SecurityReqID	x
559	SecurityListRequestType	x
1301	MarketID
1300	MarketSegmentID
	UnderlyingInstrument		Specifies the underlying instrument
	DerivativeInstrument		Group block which contains all information for an option family.
762	SecuritySubType
15	Currency
58	Text		Comment, instructions, or other identifying information.
354	EncodedTextLen		Must be set if EncodedText field is specified and must immediately precede it.
355	EncodedText		Encoded (non-ASCII characters) representation of the Text field in the encoded format specified via the MessageEncoding field.
336	TradingSessionID		Optional Trading Session Identifier to specify a particular trading session for which you want to obtain a list of securities that are tradeable.
625	TradingSessionSubID
263	SubscriptionRequestType		Subscribe or unsubscribe for security status to security specified in request.
	StandardTrailer	x

Notes

Please post comments, clarifications, examples here. Click on the edit button on the right and away you go! 

Don't forget to refer to the FPL Discussion Groups to back up anything you write.
You will often find the authoritative statements on matters of FIX specification interpretation there.
Links from FIXwiki pages to relevant discussions on the FPL site are very valuable.

For example if you were writing a clarification on how to specify the "quantity" of an order in FIX, you might add the
following relevant link, http://www.fixprotocol.org/discuss/read/f5014573, to back up your points.