c-opt-extra-label-key

c-opt-extra-label-key is a variable defined in `cc-engine.el'.
Its value is

nil

• Automatically becomes buffer-local when set.

Documentation:
Optional regexp matching labels.
Normally, labels are detected according to `c-nonlabel-token-key',
`c-decl-prefix-re' and `c-nonlabel-decl-prefix-re'. This regexp can
be used if there are additional labels that aren't recognized that
way.