They are definitely significant. 

value="foobar"

[download]
is not the same as 
value="foo bar"

[download]

And XML parsers do not return the same for 

value="foo bar"

[download]
and 
value="foo  bar"

[download]

You might be thinking of HTML's whitespace collapsing rules. Even then, that's for rendering, and attributes aren't rendered.

In reply to Re^5: Scrubbing XML by ikegami
in thread Scrubbing XML by the.duck

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