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15.6% of invalid XML feeds contain invalid characters for UTF-8 set

Google Reader team listed the top errors for XML feeds provided by various Web publishers. 15.

Google Reader team listed the top errors for XML feeds provided by various Web publishers. 15.6% of erroneous feeds claim to be UTF-8, but then contain invalid characters. 14.9% have mismatching opening and closing tags. 13.9% use undefined entities and 7.8% do not start with <.