You can split the workspace into two frames by clicking on the [S] button; then you are allowed to perform two actions independently.
For instance, you may learn how to use Markup Shredder by loading this handbook into the right frame, while you can still view, browse, edit, analyse, typeset or read your document at the left-hand side. Similarly, you may study the analysis or typesetting log on one side and view or edit your markup file on the other.
Press [J] to join both frames again.