In the screenshot below, we've created a new node with a @clean directive with a file name. We've pasted the contents of the file into the node.
This is a Vuejs component file, with three sections. We're going to break the sections out into separate nodes. First create a section name using double angle brackets.
Now select the section name plus the code you want to put in a sub node.
Enter Cmd-Shift-D to chunk the selected content into a subnode.
Repeat this process with the other sections of the Vuejs component, now each has its own node.
This is a simple example, but using Leo it is possible to quickly break up a large, complex set of code into manageable pieces. The target file is not affected, and if the target file is changed in another program, Leo will update the appropriate nodes.