Quotation marks are written as a pair of opening and closing marks in either of two styles: or . Opening and closing quotation marks may be identical in form (called neutral, vertical, straight, typewriter, or "dumb" quotation marks), or may be distinctly left-handed and right-handed (typographic or, colloquially, curly quotation marks); see quotation mark glyphs for details. Typographic quotation marks are usually used in manuscript and typeset text. Because typewriter and computer keyboards lack keys to directly enter typographic quotation marks, much of typed writing has neutral quotation marks. Some computer software has the feature often called "smart quotes" which can, sometimes imperfectly, convert neutral quotation marks to typographic ones.