17238989_Intel__Debugger__IDB__Manual__Meaning
[Convention] foo_bar : item1 | item2 | item3 [Meaning] 
A colon (:) starts the syntax definition of a non-terminal name (in this example, foo_bar. Vertical bars (|) separating items that appear in syntax definitions indicate that you choose one item from among those listed.
Intel® Debugger (IDB) Manual
Meaning