[css3-columns] Ambiguous term "constrained" for column-fill

The spec says "In continuous media, this property will only be consulted if
the length of columns has been constrained. Otherwise, columns will will
automatically be balanced."

What exactly does it mean for column length to be constrained? Clearly an
outer page height or outer column length can constrain the column length,
but if the columns' content fits into a shorter length, are these columns
actually "constrained"? For example, if I have a large page containing
<div style="column-count:2; column-fill:auto;">Hello<br>Kitty</div>
is the content balanced or is it all placed in the first column?

Similar questions apply to "min-height", "height" and "max-height". Do they
count as "constraining" column lengths, and are they "constraining" whenever
they're specified, or only when the column element height is actually
affected by those values?

Rob
-- 
"He was pierced for our transgressions, he was crushed for our iniquities;
the punishment that brought us peace was upon him, and by his wounds we are
healed. We all, like sheep, have gone astray, each of us has turned to his
own way; and the LORD has laid on him the iniquity of us all." [Isaiah
53:5-6]