The High Surrogates block spans U+D800–U+DB7F, 896 codepoints in Plane 0 (Basic Multilingual Plane).
These codepoints are not characters. In UTF-16, a high surrogate (U+D800–U+DBFF) is always followed by a low surrogate to encode one supplementary-plane character, and they are invalid anywhere else — including in UTF-8. See surrogate pairs.