Adding elements (tags) would typically be used only in an in-house situation where both the writing application and the reading application have prior knowledge of the new tags.

只有在内部环境允许的情况下，比方读写两方都对新的标签能够理解时，才会用到新元素(标签)的添加。

youdao

The meeting started in the White House Situation Room, in the basement of the West Wing.

会议在白宫西侧地下室的情况室召开。

youdao

President Obama and 18 members of his national security team spent about three hours in the White House Situation Room Wednesday, assessing their Afghanistan policy.

VOA: standard.2009.10.01

It was a different era. But General Myers spent many hours in the White House Situation Room, working with Bush administration officials on strategy for the two conflicts, just as current top officers are working with President Barack Obama and his team now on how to move forward in Afghanistan.

VOA: standard.2009.10.16

But many analysts also say that may be a temporary situation, because they don't expect the measure to be taken up by the full House of Representatives.

VOA: standard.2010.03.19

The White House Situation Room received the Homeland Security warning at 1:47 a.m. on August 29, Lieberman said.

CNN: Lieberman: White House hindering Katrina probe

All of this is of priority interest because the NSC conducts its meetings in the White House Situation Room.

FORBES: Move up http://i.forbesimg.com t Move down

Any U.S. official or agency with the proper clearance, including the White House Situation Room, State Department, CIA, Pentagon and others could continuously call up that video on their computers.

FORBES: Benghazi Stand Down Denials Don't Stand Up To Reason