@Override public void visitXmlProcessingInstruction(XmlProcessingInstruction processingInstruction) { super.visitXmlProcessingInstruction(processingInstruction); PsiElement parent = processingInstruction.getParent(); if (parent instanceof XmlProlog && processingInstruction.getText().startsWith("<?xml")) { for (PsiElement e = PsiTreeUtil.prevLeaf(processingInstruction); e != null; e = PsiTreeUtil.prevLeaf(e)) { if (e instanceof PsiWhiteSpace && PsiTreeUtil.prevLeaf(e) != null || e instanceof OuterLanguageElement) { continue; } PsiElement eParent = e.getParent(); if (eParent instanceof PsiComment) e = eParent; if (eParent instanceof XmlProcessingInstruction) break; addToResults( HighlightInfo.createHighlightInfo( HighlightInfoType.ERROR, e, XmlErrorMessages.message("xml.declaration.should.precede.all.document.content"))); } } }