[General meaning in software]
[much used in Tcl]
In Tcl, to enhance a core command by renaming the core command to be enhanced, then creating a procedure with the same name as the core command, adding the desired functionality.
Easy example, provided by RS:
rename exit _exit
proc exit {{code 0}} {
set fp [open test a]
puts $fp "trapped exit at [clock format [clock seconds]]"
_exit $code
}[General case needs uplevel ...]