boxplot statistics

From: Graham Williams

Received Tue 04 Oct 2005  7:26pm +1000 from Karin Lagesen:

I have read and reread the boxplot and the boxplot stats page, and I
still cannot understand how and what boxplot shows. I realize that
this might be due to me not knowing enough statistics, but anyway...

First, how does boxplot determine the size of the box? And 

is the line

inside the box the mean or the median (or something completely
different?) And how does it determine how long out the 

whiskers should

go?

Also, the boxplot.stats page talks about "hinges", what are those?  
"The two "hinges" are versions of the first and third 

quartile, i.e.,

close to 'quantile(x, c(1,3)/4)'."

Wikipedia has a reasonable description

   http://en.wikipedia.org/wiki/Boxplot