Cannot drag test object from left side in custom keyword script like in normal test case script

I can drag a test object in normal test case script to add it quickly, but while creating custom keyword, it is not possible. I have to type it.

I want to create a global method that can be used anywhere in my project. Don’t want to limit it to one particular test case. I know that I could create a test case and call it but wanted to do it using custom keyword.