How to splits a quad element into two trias by control?

Hi,

Thanks to all of you for your valuable time and efforts putting in helping others.

I want to spit the quad element by control,for example,the spit line is created by two points i choose.

The command i find in api are:

*elementmarksplit mark_id crosscode crosscode_size

However,this two commands spit element automatically,not under control.

Does it have other commands i do not find?

Thank you very much!!!