public String[] knownNamespaces() {
   final PsiElement parentElement = getParent();
   BidirectionalMap<String, String> map = initNamespaceMaps(parentElement);
   Set<String> known = Collections.emptySet();
   if (map != null) {
     known = new HashSet<String>(map.values());
   }
   if (parentElement instanceof XmlTag) {
     if (known.isEmpty()) return ((XmlTag) parentElement).knownNamespaces();
     ContainerUtil.addAll(known, ((XmlTag) parentElement).knownNamespaces());
   } else {
     XmlExtension xmlExtension = XmlExtension.getExtensionByElement(this);
     if (xmlExtension != null) {
       final XmlFile xmlFile = xmlExtension.getContainingFile(this);
       if (xmlFile != null) {
         final XmlTag rootTag = xmlFile.getRootTag();
         if (rootTag != null && rootTag != this) {
           if (known.isEmpty()) return rootTag.knownNamespaces();
           ContainerUtil.addAll(known, rootTag.knownNamespaces());
         }
       }
     }
   }
   return ArrayUtil.toStringArray(known);
 }
  private static Pair<Set<String>, Set<TextWithImports>> findReferencedVars(
      Set<String> visibleVars, SourcePosition position) {
    final int line = position.getLine();
    if (line < 0) {
      return Pair.create(Collections.<String>emptySet(), Collections.<TextWithImports>emptySet());
    }
    final PsiFile positionFile = position.getFile();
    if (!positionFile.getLanguage().isKindOf(JavaLanguage.INSTANCE)) {
      return Pair.create(visibleVars, Collections.<TextWithImports>emptySet());
    }

    final VirtualFile vFile = positionFile.getVirtualFile();
    final Document doc =
        vFile != null ? FileDocumentManager.getInstance().getDocument(vFile) : null;
    if (doc == null || doc.getLineCount() == 0 || line > (doc.getLineCount() - 1)) {
      return Pair.create(Collections.<String>emptySet(), Collections.<TextWithImports>emptySet());
    }

    final TextRange limit = calculateLimitRange(positionFile, doc, line);

    int startLine = Math.max(limit.getStartOffset(), line - 1);
    startLine = Math.min(startLine, limit.getEndOffset());
    while (startLine > limit.getStartOffset() && shouldSkipLine(positionFile, doc, startLine)) {
      startLine--;
    }
    final int startOffset = doc.getLineStartOffset(startLine);

    int endLine = Math.min(line + 2, limit.getEndOffset());
    while (endLine < limit.getEndOffset() && shouldSkipLine(positionFile, doc, endLine)) {
      endLine++;
    }
    final int endOffset = doc.getLineEndOffset(endLine);

    final TextRange lineRange = new TextRange(startOffset, endOffset);
    if (!lineRange.isEmpty()) {
      final int offset =
          CharArrayUtil.shiftForward(doc.getCharsSequence(), doc.getLineStartOffset(line), " \t");
      PsiElement element = positionFile.findElementAt(offset);
      if (element != null) {
        PsiMethod method = PsiTreeUtil.getNonStrictParentOfType(element, PsiMethod.class);
        if (method != null) {
          element = method;
        } else {
          PsiField field = PsiTreeUtil.getNonStrictParentOfType(element, PsiField.class);
          if (field != null) {
            element = field;
          } else {
            final PsiClassInitializer initializer =
                PsiTreeUtil.getNonStrictParentOfType(element, PsiClassInitializer.class);
            if (initializer != null) {
              element = initializer;
            }
          }
        }

        //noinspection unchecked
        if (element instanceof PsiCompiledElement) {
          return Pair.create(visibleVars, Collections.<TextWithImports>emptySet());
        } else {
          VariablesCollector collector =
              new VariablesCollector(visibleVars, adjustRange(element, lineRange));
          element.accept(collector);
          return Pair.create(collector.getVars(), collector.getExpressions());
        }
      }
    }
    return Pair.create(Collections.<String>emptySet(), Collections.<TextWithImports>emptySet());
  }