In UTF-16, most Unicode characters can be represented with a single 16-bit code unit. Only characters in the range 0x10000 to 0x10FFFF must be represented with a surrogate pair of two UTF-16 code units. RWUCharTraits provides the static method RWUCharTraits::requiresSurrogatePair(), which returns true if a given RWUChar32 code point requires a surrogate representation.

Similarly, RWUCharTraits::isHighSurrogate() returns true if a given RWUChar16 code unit is the first, or high, code unit of a surrogate pair. A high surrogate has a value in the range U+D800 to U+DBFF. The function RWUCharTraits::isLowSurrogate() returns true if a given RWUChar16 code unit is the second, or low, code unit of a surrogate pair. A low surrogate has a value in the range U+DC00 to U+DFFF. The method RWUCharTraits::isSurrogate() returns true if a given RWUChar16 is a surrogate in the range U+D800 to U+DFFF. Surrogates are not characters themselves; they are reserved for use as the low or high code unit in a surrogate pair.

Finally, RWUCharTraits::isSingle() returns true if a given RWUChar16 code unit corresponds to a single code point, or false if the value is part of a surrogate pair.