SHIFT+UP & SHIFT+DOWN keystrokes can be used to expand the selection to the previous or next line respectively.
However SHIFT+DOWN fails to extend the selection past an empty line.
SHIFT+UP appears to work as expected
Given the following text, and the caret positioned at the start of the TextArea, the first press of SHIFT+DOWN will select 'abc', the second will also select 'def', but third and subsequent presses will have no effect due to an empty 3rd line.
Workaround by using the mouse, or SHIFT+LEFT & SHIFT+RIGHT