Explain plan information provides a graphical representation of the parse tree for a CONTAINS query expression. You can obtain this information programatically with the CTX_QUERY.EXPLAIN procedure.
Explain plan information tells you how a query is expanded and parsed without having the system execute the query. Obtaining explain information is useful for knowing the expansion for a particular stem, wildcard, thesaurus, fuzzy, soundex, or ABOUT query. Parse trees also show the following information:
Order of execution
ABOUT query normalization
Query expression optimization
Stop-word transformations
Breakdown of composite-word tokens for supported languages
Oracle Text Reference for more information about using CTX_QUERY.EXPLAIN