A demand guarantee is enforceable notwithstanding any deficiencies in the enforceability of the underlying obligation. To date, there is no case law regarding the validity and enforceability of CBAs. The enforceability of these agreements depends on the law of the particular state. Clearance opinions may be done in combination with a "validity and enforceability" opinion. In Virginia, the enforceability of covenants not to compete is governed by common law principles. Within the EU, the enforceability of mediation agreements is ruled by Directive 2008/52/EC. The enforceability of the automatic renewal clause varies between countries. But the enforceability of any judgment would be a relevant consideration. The enforceability of end-user license agreements is sometimes questioned. The enforceability of non-compete agreements in the state of Florida is quite common. There are certain exceptions to enforceability of due-on-sale clauses. Mobigame's lawyers disputed the enforceability of Langdell's trademark and details of Langdell's claimed communications. Rules regarding enforceability of derivative contracts have to be laid down. Clickwrap licenses must still meet the criteria for enforceability of a unilateral form contract. Paradoxically, his copyleft approach relies on the enforceability of the copyright to be effective.