Earlier quoted context omitted.
As suggested by a sibling comment the key isn't to prevent horizontal scrolling, but to prevent content from overflowing a single screen width. Which isn't hard per se but doesn't have a one-size-fits-all solution.
So many websites overflow a single screen width by a trivial amount. This is just enough to cause accidental horizontal scrolling which disrupts the flow of scrolling the page. Very frustrating!
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Which is not being allowed to break to a new line because it doesn't contain whitespace. A CSS rule can be used to allow it to break, though that can also have other, unwanted ramifications.