Additional OpenType features include subscript/superscript. OpenType features include subscript and superscript. OpenType features include fractions, ligatures, ordinals, stylistic alternates and subscript/superscript. They may also include separate styles for superscript and subscript digits. Each superscript or subscript character is preceded by a normal "x" to show the subscripting/superscripting. This meant that the same matrix could be used for both superscript and subscript numbers. Often superscript plus and minus symbols are used to denote relative doping concentration in semiconductors. The caret is also now used to indicate a superscript in TeX typesetting. Compare also for the digraph "nn", with the tilde as a superscript . Positive and negative sets are sometimes denoted by superscript plus and minus signs, respectively. An apostrophe, , is a shortcut for a superscript prime; e.g., appears as formula 3. Approximately twenty pharyngealized consonants (marked with superscript ) also appear in the table above. Also, the ordinal indicators should be distinguishable from superscript characters. Attempting to write formula 45 using the familiar superscript notation gives a power tower. The Vancouver system uses sequential numbers in the text, either bracketed or superscript or both.