How Do You Say "Fourth Amendment" in Mexican?

So, here's a thing that happened here.  Bunch of stoner-looking guys were walking down the street, clearly guilty of being slightly unkempt, and so a cop stops them, carries out a "routine inspection" and, wouldn't ya know it - weed!  And, because this was their lucky day, it happened right where all the local news photographers hang around waiting to stenographize politicians's utterances. Bummer, dudes!

 
Let's put aside for now their mistake in breaking Burro Hall's Golden Rule #1 For Living in Mexico: "Never ever be in possession of any drugs, ever - whatta you, fuckin' stupid? You see Midnight Express? Yeah, we know it's Turkey - don't be a smart-ass." Instead, we're curious about the "routine inspection" part. We've tried a couple of times to read the State Civil Code [pdf], but it turns out to be just as impenetrable as an American legal code, only in Spanish. So here's our question for locals, Mexicans or people who are simply smarter than us (that would be all of you who live east of the Sea of Cortes): cops can just stop you and go through your shit? Seriously - one of the hardest things for a foreigner here is figuring out what his rights are. Does the fact that a dude smells like patchouli constitute probable cause? Or can cops just make this stuff up?

[Clarification:  Despite the poor phrasing, we're asking about Mexicans' rights.  We assume foreigners' rights are whatever the police say they are at any given moment (hence, Golden Rule #1 above), but if we were going to act under the assumption that most cops don't actually know the law very well (this has been our experience whenever we've had a run-in), what's the actual law as regards unwarranted searches and seizures on the street?]