I am very sorry if this has already been asked, and I did look in the documentation, but couldn't find my answer : 

I understand how to write macros accepting several arguments, but what I am missing is a simple way to enter the arguments when you invoke the macro.

 For example, in a macro like :

<assign|s|<macro|from|to|<below|<above|<big|sum>|<arg|to>>|<arg|from>>>>

I would like to be able to write something like <\s i=1 n> to display the sum from i=1 to n, which would be a considerable gain of time, especially for more complex macros involving several subscripts/superscripts, punctuation... in which navigating to the argument's placeholder with the arrow keys is not very efficient. Is there such a way to proceed?

Thanks in advance!