Understanding Table Editioning

I am trying to understand the internals of editioning of standard tables in R12.2 after online enablement. When a standard table such as fnd_concurrent_processes is altered to extend a column during patching, a new column with #1 is created for the column in the same table and apps synonym points to the #1 column. How does it copy the data from the standard (old) column to the #1 column and at what point? Does it use cross edition triggers, I don't find any such triggers for the table. Please let me know if you have the insight of it.