Rules should not search inside attributes

[CordyJ]

Attributes are not part of the source being transformed, rather annotations on it. Thus rules and functions should not search inside anything of type [attr X] for any [X]. If internal transforming of attributes is required, they can be explicitly matched and rules applied inside them.

[CordyJ]

This can be achieved using multi-skipping, since the overall performance cost would be high to implement this otherwise. If we want to skip an attribute [attr X], we just change it to [attr attr_X], and use skipping [attr_X].