Although there is an image in this APP's homepage, somewhat showing the splitting view of source files(, well it is actually the comparing view of a given file in version control, used for an analogy), I don't know how to really activate the splitting view of one file in my real usage of this APP.
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I tried to search all that may be related in current workspace window, whereas resulting in the buttons that were off-topic. I'm not sure whether there is anything missed.
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In that case, the 'New Window' button just leads to an extra new windows of this APP instead of splitting files in the original window.