Eg. allow ${FOOBAR:barfoo} `${FOOBAR:barfoo}` -> if env `FOOBAR` is not set, use `barfoo` as value `${FOOBAR::barfoo}` -> if env `FOOBAR` is not set or set and empty, use `barfoo` as value
Eg. allow ${FOOBAR:barfoo}
${FOOBAR:barfoo}-> if envFOOBARis not set, usebarfooas value${FOOBAR::barfoo}-> if envFOOBARis not set or set and empty, usebarfooas value