Indicates whether the specified char object is a high surrogate.
true if the numeric value of the c parameter ranges from U+D800 through U+DBFF; otherwise, false.
In addition to representing single characters using a 16-bit code point, UTF-16 encoding allows abstract characters to be represented using two 16-bit code points, which is known as a surrogate pair. The first element in this pair is the high surrogate. Its code point can range from U+D800 to U+DBFF. An individual surrogate has no interpretation of its own; it is meaningful only when used as part of a surrogate pair.