XML declaration allowed only at the start of the document
No whitespace, comments or second declaration may precede an XML declaration. Remove duplicated declarations when combining fragments and retain one document root. Check the exported bytes and encoding.
Move the declaration to the beginning
No whitespace, comments or second declaration may precede an XML declaration. Remove duplicated declarations when combining fragments and retain one document root. Check the exported bytes and encoding.
Reproduced engine diagnostics and complete fixes
Original minimal examples checked on 2 November 2026. Engine wording differs; follow the cause, not a message alone.
libxml2-wasm 0.7.2
XML declaration allowed only at the start of the documentXerces2-J 2.12.2 / Temurin Java 21.0.13+9-LTS
The processing instruction target matching "[xX][mM][lL]" is not allowed.lxml 6.0.2 / libxml2 2.14.6
XML declaration allowed only at the start of the document.NET 10.0.14 / System.Xml
Unexpected XML declaration. The XML declaration must be the first node in the document, and no whitespace characters are allowed to appear before it. Line 2, position 3.Repeat this check in your workflow
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