You can only select text in the work window's source view (right-hand section).
The use of a block structure results in a few peculiarities concerning the selection of text:
You can make a selection covering several blocks, but only the lines of text will be selected.
Text lines in collapsed blocks will be ignored.
In short, only visible text lines can be included in a selection. Only visible text lines can be handled using the clipboard functions (Cut, Copy, Paste and Delete).