It is implemented as a backend for the Perl compiler. Each File section reports on a single file. These report, respectively, on subroutine definitions found by the initial symbol table walk and on the main part of the program or module external to all subroutines.
Lexical variables are easier to track and even included dereferencing information where possible.
Simple uses aren't preceded by a code letter. The t option prints the object on the top of the stack as it's being tracked. The O option prints each operator as it's being processed in the execution order of the program. BUGS Non-lexical variables are quite difficult to track through a program. Sometimes the type of a non-lexical variable's use is impossible to determine.