The &Attribute-Name Operator
&Attribute-Name operator returns a reference to the named attribute.
When used as an existence check, the condition evaluates to
the attribute exists. Otherwise, the condition evaluates to
Older versions of the server did not use the
& character. Version 3
does not require it, but a warning will be printed in debugging mode if the
& is omitted.
& character was added in version 3 in order to disambiguate the
unlang. Previously, older versions of the server could
interpret a string such as
hello-there either as a literal string
"hello-there", or as a reference to an attribute named
hello-there. This ambiguity caused problems.
Adding the leading
& character means that attribute references are
now easily distinguishable from literal strings.