why is $.support being populated in transit.js

why is $.support being populated in transit.js

hey guys , good day , have a look at the below function :: 

  1.   for (var key in support) {
  2.     if (support.hasOwnProperty(key) && typeof $.support[key] === 'undefined') {
  3.       $.support[key] = support[key];
  4.     }
  5.   }
i see the for in loop being used and the $.support method in jQuery being populated with more properties. WHY ? 

I fund the above function here .