minus sign before python method

minus sign before python method

i've been reading through the ocstyle source code and i ran into methods
that have '-' before them. here's is an example
@rule(modifier[...] + (sizedCType | anyIdentifier) + -implementedProtocols +
(Present(Regex(r'[(),<>:]')) | sp(1)) + Literal('*')[...])
there are times that methods have a '-' before the method call right
before it returns. is there anyone who can identify what this is called or
point me to some other resource? i've tried looking for it and came to the
conclusion here would be my best bet.