The section http://documentation-devel.engineering.redhat.com/docs/en-US/JBoss_Enterprise_Application_Platform/6/html-single/Administration_and_Configuration_Guide/index.html#Configure_Logging_for_the_Transaction_Subsystem1
contains description of log levels used for TM. The list is not complete. TRACE level should be added under title "Transaction Logging Levels, from Most to Least Verbose".
*** Bug 887292 has been marked as a duplicate of this bug. ***
I've checked the doc and it's fine now. Thanks.