one of the documented procedures in this installation of the ACS
ad_custom_load   db   user_id   item_group   item   item_type
What it does:
load a persisted user customization as saved by for example table-custom.tcl.
Defined in: /web/philip/packages/acs-core/table-display-procs.tcl

Source code:

    util_dbq {item item_group item_type}
    set selection [ns_db 0or1row $db "select value_type, value from user_custom 
    where user_id = $user_id and item_type = $DBQitem_type
    and item_group = $DBQitem_group and  item = $DBQitem"]
    if {![empty_string_p selection]} { 
        # should check value type in ns_set etc. and create the 
        # correct data type
        if {[catch {eval set value "{[ns_set value $selection 1]}"} errmsg]} {
            set value {}
    } else { 
        set value {}
    return $value