You can't safely send zero bytes over XML even with UTF-8 encoding. Not in practice: echo '<zero></zero>' | xmllint - -:1: parser error : xmlParseCharRef:

You can't safely send zero bytes over XML even with UTF-8 encoding. Not in practice: echo '<zero></zero>' | xmllint - -:1: parser error : xmlParseCharRef: invalid xmlChar value 0 <zero></zero> ^ printf '<?xml version="1.0" encoding="utf-8"?><zero>\0</zero>' | xmllint - -:1: parser error : Premature end of data in tag zero line 1 <?xml version="1.0" encoding="utf-8"?><zero> ^ And not in theory: https://www.w3.org/TR/2006/REC-xml11-20060816/#sec-well-formed https://www.w3.org/TR/2006/REC-xml11-20060816/#sec-well-form... Character Range [2] Char ::= [#x1-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF] /* any Unicode character, excluding the surrogate blocks, FFFE, and FFFF. */ [2a] RestrictedChar ::= [#x1-#x8] | [#xB-#xC] | [#xE-#x1F] | [#x7F-#x84] | [#x86-#x9F]