A module developer cannot add anything to the blockform in block edit_func.
more specifically it cannot add customValidationCode to xoopsFormValidate_blockform
eg: we cannot make any option as Required because it will not added the js to blockform onsubmit.
I consider it a serious bug that should be addressed in 2.6
I dont know what is the final solution.
maybe we need a specific XoopsBlockForm class because the current one in 2.6 is nothing more than a simple renderer.
more discussion here: