Function assignmentInternalHandler 

pub fn assignmentInternalHandler<T>(
    c: Configuration<T>,
    v: Variables<'_, T>,
    t: TokenStream,
    interp_first: bool,
    interp_after: bool,
) -> Result<(Variables<'_, T>, TokenStream), (Variables<'_, T>, TokenStream)>
where
    T: StartMarker + Clone,