An instance is an interacting entity of an MSC. Events are on instances and they are ordered according to their position on the instance from top to bottom. An instance has an instance head and an instance end or a stop. Between these there is the instance axis which may be either a single vertical line or a column defined by two vertical lines.

<instance area> ::=

<instance head area> is followed by <instance body area>

<instance head area> ::= <instance head symbol>

is associated with <instance heading>

[ is attached to <createline symbol>]

<instance heading> ::=

<instance name> [[:]<instance kind>][decomposition>]

<instance body area> ::= <instance axis symbol>

is followed by {<instance end symbol>|<stop symbol>}