jQuery expando properties
Question 3 seems out of place but for the rest:
jQuery.expandois a string which is basically'jQuery' + uniqueid(just a unique value)
Prior to version 1.4.4, the uniqueid is current timestamp.
After that from version 1.5.1, the uniqueid is version+Math.random() with dots replaced. To be clear, "jQuery" + ( version + Math.random() ).replace( /\D/g, "" ).
jQuery.cacheis an object that will store the data valuesElement[ jQuery.expando ]is a int value/key that is where the object is stored injQuery.cachejQuery.cache[ Element[ jQuery.expando ] ]is an object of that elements data props