ISO/IEC 14651:2016, Information technology -- International string ordering and comparison -- Method for comparing character strings and description of the common template tailorable ordering, is an ISO Standard specifying an algorithm that can be used when comparing two strings. This comparison can be used when collating a set of strings. The standard also specifies a datafile specifying the comparison order, the Common Tailorable Template, CTT. The comparison order is supposed to be tailored for different languages (hence the CTT is regarded as a template and not a default, though the empty tailoring, not changing any weighting, is appropriate in many cases), since different languages have incompatible ordering requirements. One such tailoring is European ordering rules (EOR), which in turn is supposed to be tailored for different European languages.
The Common Tailorable Template (CTT) datafile of this ISO Standard is aligned with the Default Unicode Collation Entity Table (DUCET) datafile of the Unicode Collation Algorithm (UCA) specified in Unicode Technical Standard #10.
This is the fourth edition of the standard and was published on 2016-02-15, corrected on 2016-05-01 and covers up to and including Unicode 8.0. One additional amendment Amd.1:2017 was published in September 2017 and covers up to and including Unicode 9.0.