Function opt_dot_keys 

fn opt_dot_keys(
    tokens: &mut TokenSlice<'_, Token>,
    receiver: &mut dyn EventReceiver,
    error: &mut dyn ErrorSink,
) -> bool

Start a key from the first key compatible token type

Returns the last key on success

This will swallow the trailing TokenKind::Whitespace

key = simple-key / dotted-key
simple-key = quoted-key / unquoted-key

quoted-key = basic-string / literal-string
dotted-key = simple-key 1*( dot-sep simple-key )

dot-sep   = ws %x2E ws  ; . Period