In Workflowy it looks like you can insert a line-break from a top level node via shift-enter, you can replicate this in Text Blaze with the key command:
For example:
Top level text{key: shift-enter}More text on a new line that won't be made into a new node
@Dave_Zoo_Logical, I confirm that Scott's suggestion works. I've just tested it myself.
Item main{key: shift-enter}Item sub
Not that you should keep the command on the same line, otherwise you'll get extra line breaks, which you don't want.
HOWEVER, here's a little hack for you. If you want a more understandable snippet, you can put line breaks and then use the trim setting to get Text Blaze to clean them when it renders the snippet.
See my example below. Also, try changing trim=yes to: