As you know, all MXML files are converted to ActionScript Classes which are later compiled in SWF file. If you want to view / study these automatically generated classes, you can use Compiler Argument -keep-generated-actionscript in Flex Builder Project.

In Flex Builder navigate to Project > Properties > Flex Compiler > Additional compiler arguments and add following configuration: -keep-generated-actionscript

This will create a folder named generated in project source folder which will have all ActionScript classes which Flex Builder automatically generates from MXML ({MXML file name}-generated).