${} vs. #{}

I'm new to webflow and I'm trying to get started with the sample applications included in the download. I'm referencing the sellItem-jsf as my application is using JSF. This may seem a rather foolish question but what is the difference between using ${variable} vs. #{variable}?

In the spring webflow reference guide it makes reference to:

Quote:

The DelegatingFlowVariableResolver resolves JSF a value binding expression like
{#someBean.someProperty} to a flow execution attribute.

(which I know to be a typo. It should be #{someBean.someProperty})
but all the sample applications seem to be using ${someBean.someProperty}. It seems to make a difference because if I change the jsp pages to use the #{someProperty} syntax the results are not what is expected.

It there somewhere that this value is set for the expression language? Should I even concern myself with this?

Thanks for the help...