code: protected void appendProcessingInstruction(StringBuilder sb, ProcessingInstruction instr) {
          sb.append("<?")
              .append(instr.getTarget())
              .append(' ').append(instr.getData())
              .append("?>");
      }
docs: Formats a processing instruction for {@link #getShortString}.
  
  @param sb the builder to append to
  @param instr the processing instruction
  
  @since XMLUnit 2.4.0