Hi, Christian,
Thanks very much for looking into this. If I use the OxGarage TEI web service through the front-end client to upload a file (http://www.tei-c.org/oxgarage/), here is how it sends the request payload on the back end. Non-ASCII characters are replaced with octal escape sequences.
Encapsulated multipart part: (text/xml)
Content-Disposition: form-data; name="fileToConvert"; filename="tei.xml"\r\n
Content-Type: text/xml\r\n\r\n
eXtensible Markup Language
<TEI xmlns="http://www.tei-c.org/ns/1.0" xml:lang="en">
<teiHeader>
<fileDesc>
<titleStmt>
<title>Multipart test</title>
<author/>
</titleStmt>
<publicationStmt>
<p>unknown</p>
</publicationStmt>
<sourceDesc>
<p>unknown</p>
</sourceDesc>
</fileDesc>
</teiHeader>
<text>
<body>
<div type="level1">
<div type="level2">
<p n="4">
<hi rendition="simple:bold"/>
</p>
<p n="5" rend="Normal">
<hi rend="bold underline"> Regression Equation </hi>
</p>
<p n="6" rend="Normal">
<math xmlns="http://www.w3.org/1998/Math/MathML">
<mover accent="true">
<mrow>
<mi> Y </mi>
</mrow>
<mo> ^ </mo>
</mover>
<mo> = </mo>
<msub>
<mrow>
<mi> \316\262 </mi>
</mrow>
<mrow>
<mn> 1 </mn>
</mrow>
</msub>
<mo> + </mo>
<msub>
<mrow>
<mi> \316\262 </mi>
</mrow>
<mrow>
<mn> 2 </mn>
</mrow>
</msub>
<msub>
<mrow>
<mi> X </mi>
</mrow>
<mrow>
<mn> 2 </mn>
</mrow>
</msub>
<mo> + </mo>
<mo> \342\200\246 </mo>
<mo> + </mo>
<msub>
<mrow>
<mi> \316\262 </mi>
</mrow>
<mrow>
<mi> i </mi>
</mrow>
</msub>
<msub>
<mrow>
<mi> X </mi>
</mrow>
<mrow>
<mi> i </mi>
</mrow>
</msub>
</math>
</p>
</div>
</div>
</body>
</text>
</TEI>
Boundary: \r\n-----------------------------10775069631632435281298450283\r\n