system (type) heading

The heading of system diagrams, that is a system-heading is as follows:

<system-heading> ::= system <system-name>

while system type diagrams have system-type-headings:

<system-type-heading>::=
system type [< qualifier >] <system-type-name>
[<formal-context-parameters>]
[< specialisation >]

As indicated in the syntax rule above, a system type can have formal context parameters and it can be a specialisation (of a more general system type).