The ellipsis denotes either the omission of text or an interruption or hesitation. Although it is very common to use three periods as an ellipsis, most fonts have built-in ellipsis characters. Proper ellipsis characters are spaced out slightly more than three consecutive periods.
The HTML code for a proper ellipsis is …. Some typographers prefer to set custom ellipses by using thin spaces ( ) between periods. The general rule is to use an ellipsis that makes spacing consistent within the text block.
A hyphen is not a minus sign (− −), and neither a lowercase x nor an asterisk (*) is a multiplication sign (× ×). Using a slash for fractions does not produce the proper look of having numerator above and the denominator below, as you can see when comparing 1/2 vs. ½ (½). And the slash is not a division sign (÷ ÷ ), either.
A complete list of special characters in HTML code by W3Schools is available here.
Accent marks, or diacritics, are used in many Latin alphabet-based languages to change the sound value of the letter to which they are added. They also are used in several English words that were borrowed from other languages, such as déjà vu.
typeit.org allows people to add typographic accents and special characters directly while typing.