I use that feature when I record the Dev Meet and Greets...it's very handy but there is no filter.
Here is an example of what it saves:
[16/02/08][17:16:07] [<41213235>Naughty Dreams]: you people are mean
[16/02/08][17:16:13] [<26156212>Amethyst]: motion is closed! next order of business???
[16/02/08][17:16:24] [<26156212>Amethyst]: ahhh raphics team....hmmmmmm
[16/02/08][17:16:27] [<11590371>Buck]: i was just kidding
[16/02/08][17:16:31] [<26156212>Amethyst]: im not
[16/02/08][17:16:57] [<26156212>Amethyst]: if i DO get banned tonight, all yall take care, its been a wonderful 18 years with all yall
[16/02/08][17:17:11] [<11590371>Buck]: hehe
[16/02/08][17:17:21] [<31694912>Rauko Balrog]: want just co owner m to you home first
[16/02/08][17:17:22] [<6707324>Pit]: lol
[16/02/08][17:17:24] [<11590371>Buck]: take care if we don't c ya
[16/02/08][17:17:37] [<26156212>Amethyst]: naw EVE L will have all that mess
[16/02/08][17:17:48] [<26156212>Amethyst]: oh i will

[16/02/08][17:18:15] [<11590371>Buck]: where r ur houses so I can be there when they fall?
[16/02/08][17:19:00] [<26156212>Amethyst]: castle fel swamp tram ice isle castle another castle somwhere cant remember and the luna house
[16/02/08][17:19:26] [<26156212>Amethyst]: atl theres a 18x18 and a keep i think
[16/02/08][17:19:51] [<26156212>Amethyst]: and another castle on origin full of powerscrolls...so knock urself out
[16/02/08][17:19:59] [Pacifica]: Some of the latest news!
[16/02/08][17:19:59] [Pacifica]: Dev Meet & Greet February 8th @ 6PM PST (9PM Eastern) [Castle Blackthorn Throne Room]
As you can ~MAYBE~ tell...it logs General Chat, NPC chatter, regular chat and if you talk in guild/alliance chat it will record that too as well as any spells that you or anyone else casts.
It's rather messy to sort through but it's a VERY handy feature. There used to be a program called UO Journal that you could use with the Classic Client that worked pretty well, not sure if that still works.