White space is important in documents. In some languages, it's used to separate words. In computer files, it's commonly used to break things up and make text more readable. In typography and presentation, the effective use of white space is tremendously important.
Watch out; not all the characters that you might think of spaces count as spaces in XML. In particular, Unicode defines a few special kinds of spaces, including one called "Ideographic Space" designed for use in between Chinese, Japanese, and Korean characters. But in XML, none of them are white space in the sense this specification uses the word.
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