From the NYT:

We were in a small house in Zarqa, Jordan, trying to interview two heavily bearded Islamic militants about their distribution of recruitment videos when one of us asked one too many questions.

“He’s American?” one of the militants growled. “Let’s kidnap and kill him.”

The room fell silent. But before anyone could act on this impulse, the rules of jihadi etiquette kicked in. You can’t just slaughter a visitor, militants are taught by sympathetic Islamic scholars. You need permission from whoever arranges the meeting. And in this case, the arranger who helped us to meet this pair declined to sign off.

“He’s my guest,” Marwan Shehadeh, a Jordanian researcher, told the bearded men.

With Islamist violence brewing in various parts of the world, the set of rules that seek to guide and justify the killing that militants do is growing more complex.

This jihad etiquette is not written down, and for good reason. It varies as much in interpretation and practice as extremist groups vary in their goals. But the rules have some general themes that underlie actions ranging from the recent rash of suicide bombings in Algeria and Somalia, to the surge in beheadings and bombings by separatist Muslims in Thailand.