twitter/bootstrap — pull request #8116 by dark-cms (2013-06-09 17:30:41+00:00)
Title: Calculate position for Affix bottom

added positionbottom as Option-Value for affix()

so it is possible to calculate the css-bottom-value.
Example:
var $document = $(document);
var $Affixparent = $("#ProductDetails");

// side bar
$('#affixtocart').affix({
offset: {
top: function() { return $Affixparent.offset().top; },
bottom: function() { return $Affixparent.offset().top + $Affixparent.height()/2; }
},
positionbottom : function() {
return parseInt($document.height() - ($Affixparent.offset().top + $Affixparent.height()));
}
}

CSS:
body {position: relative}
.affix { position: fixed; top: 40px}
.affix-bottom { position: absolute}

other css-positions not needed