The result was the modern typographic grid that became associated with the International Typographic Style. Most typographic glyphs originate from the characters of a typeface. Most systems with typographic features today provide this type of kerning. German orthographic (or rather typographic) rules require that the mandatory blackletter ligatures are retained. Two major Swiss design schools are responsible for the early years of International Typographic Style. Some languages use superior letters as a typographic convention for abbreviations. Robert Bringhurst in "The Elements of Typographic Style" calls the forms "horticultural dingbats". These are limited to one typographic line of symbols, which may include subscripts and superscripts. This integrates perfectly with the type, an example of typographic art. Bester played with typographic symbols when constructing various characters' names. His work often takes the form of typographic texts. Corel's CorelDRAW introduced support for OpenType typographic features in version X6. Whitespace is a commonly used concept for a typographic effect. The same U+2019 code point and glyph is used for typographic (curly) apostrophes. Venice quickly became the center of typographic and printing activity.