OKC7 check condition

In OKC7, step 001, there is a check: BSID Account and Cost Center Validation. but when I doule click it, it doesn't show a user exit,

how can I view the content of "BSID Account and Cost Center Validation",

normally we can see check condition looks like: G/L = '42000020'

but this CO validation rule is strange, anyone can explain, thanks