The ISO/IEC International Standard 9995 specifies various characteristics of keyboards. It defines a framework for the layout of keyboards where a keyboard is divided logically into groups and levels, and physically into sections and zones.
A group is a collection of characters that logically belong together. These characters are usually arranged on up to three levels (such as level 2 for the capital forms of letters) within a group. A keyboard could have any number of groups. Typically, when more than one language is used, multiple groups are required.
The primary group or national layout that is established in most countries, by a national standard or by national usage, is assigned to group 1. Secondary groups are assigned from group 2 onwards. A user may choose to switch from the default group 1 to another group or level via the group select or level select mechanisms.
Many national keyboard standards define layouts according to ISO/IEC 9995, although some layouts fall outside of the ISO/IEC 9995 standard. Examples of this are de facto standards such as the Polish Programmer's keyboard or the Microsoft U. S. International keyboard.