How to force a line break in a long word in a DIV?

I am not sure about the browser compatibility

word-break: break-all;

Also you can use the <wbr> tag

<wbr> (word break) means: "The browser may insert a line break here, if it wishes." It the browser does not think a line break necessary nothing happens.

Use word-wrap:break-word;

It even works in IE6, which is a pleasant surprise.

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word-wrap: break-word has been replaced with overflow-wrap: break-word; which works in every modern browser. IE, being a dead browser, will forever rely on the deprecated and non-standard word-wrap instead.

Existing uses of word-wrap today still work as it is an alias for overflow-wrap per the specification.