Well, yyy..... is treated as a single unit in HTML, so it will stretch whatever DIV it's contained in, like an image that's wider than the DIV it's contained in. Regular content should have spaces between words, and in those cases, text that over flow should automatically line break to the next line.
You can use CSS to either hide single unit overflowing content, or enable horizontal scrollbars instead to accommodate it. Those are about your options though:
Code:
style="width: 300px; overflow-x: hidden;">
Change hidden to scroll if you wish to enable scrollbars instead.
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