Regular Expression Explanation for 'function.lang'

Hello,

I have made an IDL syntax highlight file:
rsiidl.lang

One of the included files is 'function.lang'.
This works fine for functions that return a value
since the call syntax for functions is:

VARIABLE = SOMEFUNC(variable , variable, ...)

I now want to define 'procedure.lang' where
the call syntax is:

SOMEPROC, variable, variable, ...

As you can see the call to a procedure in IDL does
not include parenthesis.


'function.lang' reads as follows:


vardef FUNCTION = '(?:[[:alpha:]]|_)[[:word:]]*[[:blank:]]*(?=\()'
function = $FUNCTION




What format (of regex ??) is being used here?
How might I change this to test just the 'procedure' case?

Thanks

Peter