If the documents are not visible side by side, first move the mouse pointer to the button of the target document while keeping the mouse button pressed. The document in question is then displayed and you can move the mouse pointer into the document.
如果无法同时看到这些文档，请先按住鼠标键不放，同时将鼠标指针移到目标文档的按钮上。目标文档随即显示出来，这时可以将鼠标指针移到该文档中。