In addition to b_o_leary
above, if you do not wish to include a button
in your page, but instead just a normal link
, you can do it like this:
Update: As a response to what WWWWolf said on his update above, it is not always necessary for the author of the HTML page to know where the user came from; these gimmicks are often useful because the user her/himself most likely does know where s/he came from (and if s/he wants to go back there or not).