In Florida v. Wells (1990) 495 U.S. 1, a driver was stopped for speeding and subsequently arrested for driving under the influence. He gave the highway patrol officer permission to open the trunk of his car. After Wells was arrested, his car was towed to an impoundment facility, where two marijuana cigarette butts were found in the ashtray. The arresting officer then instructed the employees of the facility to open a locked suitcase in the trunk, which contained a large quantity of marijuana. (Id. at pp. 2-3.) In holding the search invalid, Wells noted that the state highway patrol had "no policy whatever" regarding the opening of containers within an impounded vehicle. (Wells, supra, 495 U.S. at p. 4-5.) However, it emphasized that a "standardized police procedure" need not be an "all or nothing" matter. (Id. at p. 4.) The state supreme court thought Colorado v. Bertine (1987) 479 U.S. 367 forbade exercise of any discretion by the individual officer in deciding whether to open a given container. (Id. at p. 3.) But Wells held that a "police officer may be allowed sufficient latitude to determine whether a particular container should or should not be opened in light of the nature of the search and characteristics of the container itself." (Id. at p. 4.) The Court cautioned that "an inventory search must not be a ruse for a general rummaging in order to discover incriminating evidence" or "turned into 'a purposeful and general means of discovering evidence of crime.' " (Wells, supra, 495 U.S. at p. 4.) Wells made clear, however, that it forbade only "uncanalized discretion," not discretion guided by "the nature of the search and characteristics of the container." (Ibid.) Moreover, in Wells there was more evidence to suggest that the inventory search was a pretext, including that the inventory had not been conducted before the car was towed, and the suitcase in the trunk was opened only after other incriminating evidence had been found in the interior of the car. Indeed, the arresting officer blatantly betrayed his intention to search the car because he suspected it contained drugs. (Wells, 495 U.S. at p. 7 (conc. opn. of Brennan, J.).) The opinion does not indicate that a thorough inventory of the car was performed, or instead whether the search ended when the cache of marijuana was discovered. It implies, however, that a written inventory of the car's contents was never generated. (Id. at p. 6 (conc. opn. of Brennan, J.).) In light of Bertine and Wells, the California Supreme Court has observed that the prosecution may be required "to prove more than the existence of some general policy authorizing inventory searches; when relevant, the prosecution must also prove a policy or practice governing the opening of closed containers encountered during an inventory search." (Williams, supra, 20 Cal.4th at p. 138.) We do not read Williams as requiring a specific policy delineating in advance which containers may or may not be opened. Such a requirement would unduly bind the hands of law enforcement in its role as caretaker of property seized as part of a vehicle impoundment and would be inconsistent with the rule of Wells. Rather, we believe that if a law enforcement agency has trained its officers regarding the purpose of an inventory search and the types of items they should be looking for, and has provided them with a tow form upon which to record the inventory, that satisfies the requirement of a standardized procedure. Even after Williams, California courts have held that a policy regarding the opening of containers during an inventory search need not be reduced to writing and may allow for officer discretion in determining which containers should be opened. "The police may exercise discretion in opening containers during inventory searches provided that discretion is exercised according to 'standardized criteria'or 'established routine'based on some standard other than suspected criminal activity.. . . For instance, an inventory policy permitting police officers to open closed containers when unable to ascertain the contents from examining the container's exterior would not violate the Fourth Amendment." (Needham, supra, 79 Cal.App.4th at p. 266.) The majority held some degree of police discretion in opening an item found during an inventory search is entirely appropriate under the Fourth Amendment. " 'Nothing ... prohibits the exercise of police discretion so long as that discretion is exercised according to standard criteria and on the basis of something other than suspicion of evidence of criminal activity.'" (Florida v. Wells, supra, at pp. 3-4.) A mechanical rule that insists on covering all or nothing is too inflexible. "A police officer may be allowed sufficient latitude to determine whether a particular container should or should not be opened in light of the nature of the search and the characteristics of the container itself. ... The allowance of this exercise of judgment ... does not violate the Fourth Amendment." (Id. at p. 4.)