“Rule” means each agency statement of general applicability that implements, applies, interprets, or prescribes law or policy, but does not include (i) statements concerning only the internal management of an agency and not affecting private rights or procedures available to persons or entities outside the agency, (ii) informal advisory rulings issued under Section 5-150, (iii) intra-agency memoranda, (iv) the prescription of standardized forms, (v) documents prepared or filed or actions taken by the Legislative Reference Bureau under § 5.04 of the Legislative Reference Bureau Act, or (vi) guidance documents prepared by the Illinois Environmental Protection Agency under Section 39.5 or subsection (s) of § 39 of the Environmental Protection Act.