getsection is called multiple times with each individual input passed as the first expression.
localmakes the expression only usable from within the script that it is defined in. This allows you to create expression that do not interfere with expressions from other addons or scripts.
non-singleindicates that the expression may return more than one value regardless of context.
uppercase "test"would be single and
uppercase ("hello" and "world")would be non-single.