'!' and naming conventions

[cym13 via Digitalmars-d-learn]

Hello,

I see a lot of functions and other stuff with a '!' in the name
such as 'bitfields!' or 'ctRegex!'. What does it mean exactly? In
scheme, we use such a convention to warn that a function is not
pure, but I don't see the point of using it that way in D as
there are other way to express it.

Moreover, I'm looking for a style guide of D, something like the
PEP8 for python. Is there anything like that?

Thanks!