Document Concatenation Operator +

If both operand expressions are of type Document or a java.io.InputStream or a java.io.Reader, then the result is a reference to a newly created Document object that is the concatenation of the two operand documents. The content of the left-hand operand precedes the content of the right-hand operand in the newly created document. The concatenation is low-level and makes no assumptions as to the content of both documents. The resulting content type will be reported the same as the first document that defines a content type.