+/*-------------------------------------------------------------------
+LDAP/X.500 string syntax / matching rules have a few oddities. This
+comment attempts to detail how slapd(8) treats them.
+
+Summary:
+ StringSyntax X.500 LDAP Matching
+ DirectoryString CHOICE UTF8 i/e + ignore insignificant spaces
+ PrintableString subset subset i/e + ignore insignificant spaces
+ NumericString subset subset ignore all spaces
+ IA5String ASCII ASCII i/e + ignore insignificant spaces
+ TeletexString T.61 T.61 i/e + ignore insignificant spaces
+
+ TelephoneNumber subset subset i + ignore all spaces and "-"
+
+ See draft-ietf-ldapbis-strpro for details (once published).
+
+
+Directory String -
+ In X.500(93), a directory string can be either a PrintableString,
+ a bmpString, or a UniversalString (e.g., UCS (a subset of Unicode)).
+ In later versions, more CHOICEs were added. In all cases the string
+ must be non-empty.
+
+ In LDAPv3, a directory string is a UTF-8 encoded UCS string.
+
+ For matching, there are both case ignore and exact rules. Both
+ also require that "insignificant" spaces be ignored.
+ spaces before the first non-space are ignored;
+ spaces after the last non-space are ignored;
+ spaces after a space are ignored.
+ Note: by these rules (and as clarified in X.520), a string of only
+ spaces is to be treated as if held one space, not empty (which
+ would be a syntax error).
+
+NumericString
+ In ASN.1, numeric string is just a string of digits and spaces
+ and could be empty. However, in X.500, all attribute values of
+ numeric string carry a non-empty constraint. For example:
+
+ internationalISDNNumber ATTRIBUTE ::= {
+ WITH SYNTAX InternationalISDNNumber
+ EQUALITY MATCHING RULE numericStringMatch
+ SUBSTRINGS MATCHING RULE numericStringSubstringsMatch
+ ID id-at-internationalISDNNumber }
+ InternationalISDNNumber ::=
+ NumericString (SIZE(1..ub-international-isdn-number))
+
+ Unforunately, some assertion values are don't carry the same
+ constraint (but its unclear how such an assertion could ever
+ be true). In LDAP, there is one syntax (numericString) not two
+ (numericString with constraint, numericString without constraint).
+ This should be treated as numericString with non-empty constraint.
+ Note that while someone may have no ISDN number, there are no ISDN
+ numbers which are zero length.
+
+ In matching, spaces are ignored.
+
+PrintableString
+ In ASN.1, Printable string is just a string of printable characters
+ and can be empty. In X.500, semantics much like NumericString (see
+ serialNumber for a like example) excepting uses insignificant space
+ handling instead of ignore all spaces.
+
+IA5String
+ Basically same as PrintableString. There are no examples in X.500,
+ but same logic applies. So we require them to be non-empty as
+ well.
+
+-------------------------------------------------------------------*/
+