Fog cloud/solid fog/that kind of spell

[vanyell]

I am having a hard time figuring out how a fog cloud spell moves on the battlefield.

does the fog cloud grow? one reading suggests that it grows 20' in every direction every round for the spell's duration. am I reading this wrong?

the other way to read it suggests that it's a 20' radius circle that just stays there.

which one is correct? or is there a third way to look at it that I have not seen.

[Ernir]

Effect: Fog spreads in 20-ft. radius, 20 ft. high
This says what you need to know. It doesn't grow bigger than that.

The first line of each spell description is often fluff.

[faceroll]

This says what you need to know. It doesn't grow bigger than that.

The first line of each spell description is often fluff.

Spread's a mechanical term.
See here: http://www.d20srd.org/srd/magicOverview/spellDescriptions.htm#effect