Imported from previous forum
Not sure what this tag is used for…any ideas?
[Start Quote from FIX.4.2 .pdf spec (Page 15 of 281) Section on “User Defined Fields”]
The tag numbers greater than or equal to 10000 have been reserved for internal use (within a single firm) and do not need to be registered/reserved via the FIX website.
[End Quote]
Since you are talking about Tag 10442, I do not expect anybody “outside your firm” would know anything about it - it is company “confidential” information 
You can find out its usage by looking at the applications which send and receive it and “trace” thru the code (easier said than done 
Not sure what this tag is used for…any ideas?