History's most famous laws are often its shortest. The US constitution clocked in at just four pages; the 10 commandments on two stone tablets.
And the internet, while it put an infinity of content at its users' fingertips, owes its current form to just 26 words.
Section 230 of the Communications Decency Act, a 1996 US law, declares that: "No provider or user of an interactive computer service shall be treated as the publisher or speaker of any information provided by another information content provider."
Today, the language appears outdated. Nobody talks of "interactive computer services". But the principle behind those words remains central to the way today's tech giants - many of whom did not exist when the law was written - operate.
The law means that services such as Facebook, Twitter and YouTube, which host photos, videos and messages posted by users, are able to reorder, remove and hide those posts, without assuming legal liability in the same way that a newspaper would.
Without Section 230, Facebook removing a violent video, or even algorithmically sorting the most important news feed posts, could be seen as editorialising, and expose it to countless legal claims. For that reason, it has been defended enthusiastically by Silicon Valley's lobbying operation for more than two decades.
One study, commissioned by lobby group the Internet Association, claimed that the provisions were worth $44bn (£35bn) to America's annual output.
For years, other countries have adopted similar laws. In the European Union and the UK, internet platforms have also not been liable for users' content, although unlike the US they must take down illegal material if notified.
But as the internet giants become responsible for an increasing amount of communication, governments around the world are rethinking the hands-off approach to regulating social networks that has existed so far. In Britain, the Government has put forward proposals for "online harms" legislation that would end the era of self-regulation, with online companies forced to take active steps to ensure dangerous material is removed. Many European countries are proposing other measures.
This sea change worries the tech industry, which has been used to, for the most part, obeying one global rule book. The companies say having to abide by dozens of different regimes, and invest in heavily policing their platforms, would damage innovation. And America, fearing the rise of China's vision of the internet, is increasingly pushing its own agenda overseas.
Under the Trump administration, US trade representatives have begun including protections for internet companies in its trade deals, effectively exporting Section 230 to other countries. A deal struck with Canada and Mexico in 2018, and a further agreement with Japan last year, include protections mirroring those enjoyed by Facebook, Google and others in the US.
On Monday, Liz Truss, the International Trade Secretary, and Robert Lighthizer, her US counterpart, are due to kick off a second round of video-call trade talks. While tariffs, food standards and environmental standards have been put at the forefront of the negotiations, digital laws present a potential point of tension.
American trade objectives published last year proposed "rules that limit... civil liability of online platforms for third-party content", although exceptions could be made for "legitimate public policy objectives or that are necessary to protect public morals".
Tech companies forcefully pushed for these measures to be included. "It is critical that [the US] seek intermediary protections for intermediaries in a trade agreement," the Computer and Communications Industry Association said in one submission. Another body, the Computing Technology Industry Association, demanded that: "no party adopts measures that would impose liability as a publisher, creator, or speaker of information on third party distributors or intermediaries of that information." British industry group techUK also welcomed the proposals.
However, the UK's trade objectives were less enthusiastic. While not directly contradicting America's legal protections, objectives published by the Department for International Trade included ensuring "the Government maintains its ability to protect users from emerging online harms".
Damian Collins, the Conservative MP and former chairman of the digital, culture, media and sport committee, has been campaigning against the protections appearing in any deal. "If such a provision were required in the UK-US trade agreement, it would severely limit our ability to tackle online harms, as we would be prevented from creating legal liabilities, or to tackle companies failing in their duty of care to act against harmful content," he said in a speech last month.
Mr Collins told The Telegraph: "We would be open to massive legal disputes if we try to enforce any area of domestic law that conflicted with Section 230. We have to expect that the tech companies would tie the Government up in courts for years. This is something that is incompatible; I think we would end up with a system not dissimilar from the regulatory system that Mark Zuckerberg himself advocates... all we could do is check whether they're following their guidelines." He added that the proposals could also stop regulators from examining the algorithms the companies use, which would be protected by copyright provisions.
David Henig, director at the European Centre for International Political Economy and a former UK trade negotiator, says that the US has become increasingly forthright about protecting American companies in its trade deals, suggesting it is unlikely to back down. "In the past, the US wasn't quite so stern on it, now they are. Promoting US companies is a really big part of the kind of the US trade deal agenda."
Henig says the US is unlikely to back down: the Trump administration has been pushing for similar protections in other trade deals, including the EU and Kenya. Making an exception for the UK would weaken its hand in other discussions.
If British negotiators hope to push back against the proposal, however, they may have more luck through backchannel means. Despite its trade negotiators pushing for the legal protections, Section 230 is on increasingly shaky ground in the US.
Several US politicians have demanded reform of Section 230, arguing that internet platforms hide behind the protections to shirk their responsibilities to fight fake news, illegal images and sales of dangerous items. Others say the law allows companies to discriminate against right-leaning viewpoints.
"I think there's a very good chance in the next five years that Section 230 either will be repealed or significantly weakened," says Jeff Kosseff, a professor of cybersecurity law at the US Naval Academy's Cyber Science Department and an author of a book on the law. "The shorthand solution from some people on both sides is to get rid [of it]."
US politicians are now concerned that writing Section 230 into trade deals could thwart any attempt to change the law at home. "We find it inappropriate for the United States to export language mirroring Section 230 while such serious policy discussions are ongoing," Frank Pallone, the chairman of the Energy and Commerce Committee, and Greg Walden, its most senior Republican, wrote last year.
In December, Nancy Pelosi, the leader of the House of Representatives and most powerful Democrat in Washington, pushed to have the protections removed from the US agreement with Mexico and Canada. Although her request came too late, the Democrat-run House of Congress must ratify any US-UK trade deal, so the issue could well flare up again.
Enthusiasm for the law is also waning at the White House. Last month, after Twitter fact-checked two of his tweets, a furious Donald Trump signed an executive order seeking to strip social media companies of their protections if they are seen to engage in political meddling.
"Given internal fights over 230 within the US, I'm not sure how much they will [try to export Section 230] going forward," says Daphne Keller of Stanford Law School's Centre for Internet and Society.
Britain is preparing for a battle over the law that built the internet. With convenient timing, America may stop fighting for it.