Without the declaration its still well-formed.
And even if a doctype is specified, the XML declaration doesn’t affect validity of the document against the declared doctype(s).
NobbZ
dimitarvp
Well-formed, maybe, but a lot of parsers outright refuse to parse an XML without its header.
(EDIT: I was wrong, details below.)
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NobbZ
XML documents should begin with an XML declaration which specifies the version of XML being used.
“should” means, it is prefered to see it, but it is not necessary.
Of course, if you want to set up something that is different than the defaults, then you need it. But it is not required, not even for valid documents.
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dimitarvp
Yep, I know that. Last time I had to grapple with 20+ XML parsers (about 1.5 years ago) I do remember like half of them refused to parse without the header (written in several languages, not just Erlang/Elixir).
Just re-checked. :xmerl doesn’t require it at least. 
EDIT: Now that I think of it in more detail and reopened the last Elixir project where I had to deal with XML, I might have mistook the lack of the header with the lack of a root element, which is an invalid XML. The people there wanted an XML with several root elements for some reason. Yep, my mistake, the header is quite optional indeed and it’s just that some parsers choose to blow up without it.
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