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 dom::Serialize:attributeList {l} { set result {} foreach {name value} $l { append result { } $name = # Handle special characters regsub -all < $value {\<} value if {![string match "*\"*" $value]} { append result \"$value\" } elseif {![string match "*'*" $value]} { append result '$value' } else { regsub -all \" $value {\"} value append result \"$value\" } } return $result }