This syntax is used for string-valued attributes where lower-case and upper-case letters are considered equal for comparisons (e.g. "DUNDEE" and "Dundee" match). Strings stored with this syntax retain their upper- and lower-case letters; only the matching rule is different. It corresponds to X.500's Case-Ignore-String-Syntax.
Note that in a deviation from X.500 we also substitute this syntax for Telephone-Number-Syntax. Thus unlike X.500, our Directory Service will say that the telephone numbers "555-1212" and "5551212" are unequal, since they are seen only as strings. This was done only to reduce development effort, not because of any desire by Microsoft to deviate on this point.
The DS will accept any contents for a Teletex string; it will not attempt to verify that they are indeed printable. Nor will it actually perform a case conversion: as specified by X.500, it will store values as supplied without upper-casing or lower casing them. Individual attribute types may associate a minimum and maximum size with any string, and those size limits are enforced; any value outside the legal size range will not be accepted.
OM SYNTAX: String (Teletex)
MATCHES FOR EQUALITY SUBSTRINGS APPROXIMATE
::= { ms-AttributeSyntax 4 }