Blank needed here

What it means

The declaration's parts must be separated by whitespace: version, then encoding, then standalone. Writing version="1.0"encoding="UTF-8" leaves the parser with no boundary between them, and it says so in four words that name neither the declaration nor the missing space.

The line number is reliable here even when nothing else is: this can only happen on the first line, because that is the only place a declaration may appear.

What usually causes it

• String-concatenating the declaration and forgetting the separator.
• A template that emits the encoding attribute conditionally and drops the leading space with it.
• A search-and-replace across the declaration that ate the whitespace.
• Hand-editing the first line of a generated file.

How to fix it

• Put a space between each part: <?xml version="1.0" encoding="UTF-8"?>.
• Let a serializer write the declaration rather than assembling it as text.
• If the encoding really is UTF-8, drop the attribute — it is the default and cannot then be malformed.

The same error elsewhere

Different parsers, same defect. If you arrived with one of these messages, you are in the right place.

• Xerces (Java)

  White space is required before the "encoding" pseudo attribute in the XML declaration.

• expat (Python)

  XML declaration not well-formed: line 1, column 20

• .NET System.Xml

  Expected white space between attributes.