This procedure is defined in the server but not documented via ad_proc or proc_doc and may be intended as a private interface.
The procedure is defined as:
proc tdav::read_lock {uri} { set f [open [tdav::get_lock_file $uri] {CREAT RDONLY}] set s [read $f] set e "list ${s}" set l [eval $e] close $f return $l }