one of the documented procedures in this installation of the ACS
apm_source   __file
What it does:
Sources $__file in a clean environment, returning 1 if successful or 0 if not.
Defined in: /web/philip/packages/acs-core/20-apm-load-procs.tcl

Source code:

    if { ![file exists $__file] } {
	ns_log "Error" "Unable to source $__file: file does not exist."
	return 0

    # Actually do the source.
    if { [catch { source $__file }] } {
	global errorInfo
	ns_log "Error" "Error sourcing $__file:\n$errorInfo"
	return 0

    return 1