attr() is a jquery method. .attr( attributeName, value ) it assigns or changes an attribute.
‘rel’ describes the relationship between the current document and the document or anchor specified in the href attribute. We see it in <link rel="stylesheet" type="text/css" href="something.css" />, but it is misused all over. This may be one of those cases.
The attr('rel', 'gallery') is used to unite a group of images with the rel being an attribute and every image to be linked has rel set to the same value.
can you give me a comment on each of these fields
Don't have to they are explained in the documents http://fancyapps.com/fancybox/#docs