Issue with Flex Validation

I've noticed that the following CSS


..foo {
  flex: 0 1 auto;
}

passed to the CSS validator at https://jigsaw.w3.org/css-validator/ produces
the error

*auto is not a flex-flow value : 0 1 auto*


My understanding of the flex shorthand property from the w3c spec
<http://www.w3.org/TR/css-flexbox-1/#flex-property> is that it represents
three possible values, flex-grow, flex-shrink, flex-basis.

So I'm confused why an error message is produced about flex-flow. Does
anyone have any insight into this?

Regards,
Jack