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Quoting Victor's description and comments from Bug #24174: The XML specification forbids < in attribute values. Source 1: see the grammar for AttValue below. http://www.w3.org/TR/REC-xml/#sec-common-syn Source 2: http://www.w3.org/TR/REC-xml/#CleanAttrVals The XML serialization algorithm in the DOM Parsing and Serialization specification can produce < in XML attribute values. https://dvcs.w3.org/hg/innerhtml/raw-file/tip/index.html#dfn-concept-serialize-xml-attributes Specifically, step 2 substep 4 only quotes " and &. It should also quote < as <. One more note -- all browsers currently quote both < (as ^<) and > (as >) in XML attributes.
*** This bug has been marked as a duplicate of bug 24174 ***