This document defines a number of attribute types and matching rules which may be found useful across a range of applications of the Directory.Attribute types and matching rules fall into three categories, as described below.Some attribute types and matching rules are used by a wide variety of applications or are understood and/or used by the Directory itself.NOTE 1 ? It is recommended that an attribute type or matching rule defined in this Recommendation | International Standard be used, in preference to the generation of a new one, whenever it is appropriate for the application.NOTE 2 ? The attribute and context types definitions by this Recommendation | International Standard have some associated semantics. Such specifications should not be used in situations where these semantics do not apply.Some attribute types and matching rules are internationally standardized, but are application‑specific. These are defined in the standards associated with the application concerned.Any administrative authority can define its own attribute types and matching rules for any purpose. These are not internationally standardized, and are available to others beyond the administrative authority which created them only through bilateral agreement.