Base letter represents a primary difference. Set comparison level to UCOL_PRIMARY to ignore secondary and tertiary differences. Use this to set the strength of a Collator object. Example of primary difference, "abc" < "abd" Diacritical differences on the same base letter represent a secondary difference. Set comparison level to UCOL_SECONDARY to ignore tertiary differences. Use this to set the strength of a Collator object. Example of secondary difference, "�" >> "a". Uppercase and lowercase versions of the same character represents a tertiary difference. Set comparison level to UCOL_TERTIARY to include all comparison differences. Use this to set the strength of a Collator object. Example of tertiary difference, "abc" <<< "ABC". Two characters are considered "identical" when they have the same unicode spellings. UCOL_IDENTICAL. For example, "�" == "�". UCollationStrength is also used to determine the strength of sort keys generated from UCollator objects