XMLValidator does not give error if XML declaration is not at the starting of XML

[asthaaaaaa]

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Description

Input

Try to validate this XML<note><?xml version="1.0" encoding="utf-8"?>test</note>

Code

XMLValidator.validate(`<note><?xml version="1.0" encoding="utf-8"?>test</note>`)

Output

XMLValidator returns true

expected data

XMLValidator.validate should return error with message XML declaration allowed only at the start of the document.
https://github.com/NaturalIntelligence/fast-xml-parser/blob/3c9e9fe4346a3c9924d4db45e60a7a29c565caac/src/validator.js#L206C46-L206C104

Additional Notes:

fast-xml-parser/src/validator.js

Line 204 in 3c9e9fe

const tagname = xmlData.substr(start, i - start);

is the Root cause of the issue, as start = i in our case and tagname become ""

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