SOAP API query with < filter returns Error: Unexpected subelement querystring

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Question or Problem Statement:
I’m having trouble applying multiple <>= filter conditions within my SOAP API integration which produces an “Unexpected subelement querystring” in the SOAP API response from my request.  I suspect it’s due to XML formatting.  What are the escape equivalents to these dateTime filters?

Solution:
This is most often associated with use of the < or <= in a SOAP query, but here's the full list of the replacement values

&gt;      greater than
&gt;=    greater than or equal to
&lt;       less than
&lt;=     less than or equal to

Example:

<ns1:query>
      <ns1:queryString>Select Id From RatePlanCharge where EffectiveStartDate &lt; '2014-05-31T00:00:00.000'</ns1:queryString>
</ns1:query>

Supporting References:
http://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_references