Tabs make no sense to me as they're clearly control codes.

I maintain that if tabs are permitted, so are other ASCII control codes, like vertical tab, form feed (which is actually used in GNU code), and bell.

    int foo(void)
    {
    <TAB>/* <BEL><BEL><BEL> This bit is really important. */
    <TAB>...
    }
    <VT>
    int blah(void)
    {
    <TAB>...
    }
    <EOT>
    <EM>

:-)