in src/main/java/idea/plugin/psiviewer/view/EditorPsiElementHighlighter.java [120:127]
private boolean isElementInEditor(Editor editor, PsiElement psiElement) {
if (psiElement == null || PluginPsiUtil.getContainingFile(psiElement) == null) return false;
VirtualFile elementFile = psiElement.getContainingFile().getVirtualFile();
if (elementFile == null)
return false; // 20050826
VirtualFile editorFile = FileDocumentManager.getInstance().getFile(editor.getDocument());
return elementFile.equals(editorFile);
}