This is how a single source file should look like. Ahead of the detailed listing some general rules to follow when you write your own classes:
Example:
/* ************************************************************************
   Copyright:
   License:
   Authors:
************************************************************************ */
/* ************************************************************************
#require(qx.core.Assert)
#use(qx.log.Logger)
#asset(custom/*)
#ignore(foo)
************************************************************************ */
qx.Class.define("custom.Application",
{
  ...
});